Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -194,25 +194,10 @@
 ], [
 	AC_MSG_RESULT(no)
 	AC_MSG_ERROR(Compiler does not support properties!)
 ])
 
-AC_MSG_CHECKING(whether Objective C compiler supports blocks)
-old_OBJCFLAGS="$OBJCFLAGS"
-OBJCFLAGS="$OBJCFLAGS -fblocks"
-AC_TRY_COMPILE([], [
-	int (^foo)(int bar);
-	foo = ^ (int bar) { return 0; }
-], [
-	AC_SUBST(BLOCKS_FLAGS, "-fblocks")
-	AC_SUBST(OFBLOCKTESTS_M, "OFBlockTests.m")
-	AC_MSG_RESULT(yes)
-], [
-	AC_MSG_RESULT(no)
-	OBJCFLAGS="$old_OBJCFLAGS"
-])
-
 AC_CHECK_TOOL(AR, ar)
 AC_PROG_RANLIB
 AC_ARG_ENABLE(shared,
 	AS_HELP_STRING([--disable-shared], [do not build shared library]))
 AS_IF([test x"$enable_shared" != x"no"], [
@@ -1191,10 +1176,11 @@
 		;;
 	*-*-msdosdjgpp*)
 		have_processes="no"
 		;;
 	*)
+		AC_HEADER_SYS_WAIT
 		AC_CHECK_FUNCS(kill)
 
 		AC_CHECK_FUNC(posix_spawnp, [
 			AS_IF([test x"$ac_cv_func_kill" = x"yes"], [
 				have_processes="yes"
@@ -1241,10 +1227,28 @@
 		    -o x"$enable_shared" = x"no"], [
 			AC_SUBST(OBJFW_BRIDGE_STATIC_LIB, "libobjfw-bridge.a")
 		])
 	])
 ])
+
+dnl This needs to be after all other header checks, as they include unistd.h,
+dnl which in old glibc versions uses __block. This is worked around in the code
+dnl by undefining __USE_XOPEN.
+AC_MSG_CHECKING(whether Objective C compiler supports blocks)
+old_OBJCFLAGS="$OBJCFLAGS"
+OBJCFLAGS="$OBJCFLAGS -fblocks"
+AC_TRY_COMPILE([], [
+	int (^foo)(int bar);
+	foo = ^ (int bar) { return 0; }
+], [
+	AC_SUBST(BLOCKS_FLAGS, "-fblocks")
+	AC_SUBST(OFBLOCKTESTS_M, "OFBlockTests.m")
+	AC_MSG_RESULT(yes)
+], [
+	AC_MSG_RESULT(no)
+	OBJCFLAGS="$old_OBJCFLAGS"
+])
 
 AS_IF([test x"$GOBJC" = x"yes"], [
 	OBJCFLAGS="$OBJCFLAGS -Wwrite-strings -Wpointer-arith -Werror"
 
 	AC_MSG_CHECKING(whether we need -Wno-strict-aliasing due to GCC bugs)
@@ -1280,11 +1284,11 @@
 		{
 			struct objc_class *_isa;
 			Foo *_foo;
 		}
 
-		@property (readonly, retain) Foo *foo;
+		@property (readonly, nonatomic) Foo *foo;
 
 		+ (Foo *)foo;
 		@end
 
 		@implementation Foo
@@ -1355,10 +1359,21 @@
 		- (void)dealloc;
 		@end
 
 		@interface Foo: Object
 		@end
+
+		void
+		test(void)
+		{
+			if (sizeof(int) == 4)
+				__asm__ ("");
+			else if (sizeof(int) == 8)
+				__asm__ ("");
+			else
+				abort();
+		}
 
 		/*
 		 * Unfortunately, this cannot be shorter, as it only works when
 		 * it is used inside a macro.
 		 */

Index: src/OFApplication.m
==================================================================
--- src/OFApplication.m
+++ src/OFApplication.m
@@ -22,11 +22,17 @@
 
 #include <errno.h>
 #include <signal.h>
 
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #import "OFApplication.h"
 #import "OFString.h"
 #import "OFArray.h"

Index: src/OFFile.m
==================================================================
--- src/OFFile.m
+++ src/OFFile.m
@@ -20,11 +20,17 @@
 
 #ifdef HAVE_FCNTL_H
 # include <fcntl.h>
 #endif
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #include "platform.h"
 
 #ifdef OF_WII

Index: src/OFFileManager.m
==================================================================
--- src/OFFileManager.m
+++ src/OFFileManager.m
@@ -20,11 +20,17 @@
 
 #ifdef HAVE_DIRENT_H
 # include <dirent.h>
 #endif
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #ifdef HAVE_PWD_H
 # include <pwd.h>
 #endif

Index: src/OFKernelEventObserver_epoll.m
==================================================================
--- src/OFKernelEventObserver_epoll.m
+++ src/OFKernelEventObserver_epoll.m
@@ -21,11 +21,17 @@
 
 #ifdef HAVE_FCNTL_H
 # include <fcntl.h>
 #endif
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #include <sys/epoll.h>
 
 #import "OFKernelEventObserver.h"

Index: src/OFProcess.m
==================================================================
--- src/OFProcess.m
+++ src/OFProcess.m
@@ -17,24 +17,23 @@
 #include "config.h"
 
 #include <errno.h>
 #include <string.h>
 
-/* Work around __block being used by glibc */
-#ifdef __GLIBC__
-# undef __USE_XOPEN
-#endif
-
-#include "platform.h"
-
 #include <signal.h>
 
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
-#ifndef OF_WINDOWS
+#ifdef HAVE_SYS_WAIT_H
 # include <sys/wait.h>
 #endif
 
 #ifdef HAVE_SPAWN_H
 # include <spawn.h>

Index: src/OFStdIOStream.m
==================================================================
--- src/OFStdIOStream.m
+++ src/OFStdIOStream.m
@@ -14,20 +14,20 @@
  * file.
  */
 
 #include "config.h"
 
-/* Work around __block being used by glibc */
-#include <stdlib.h>	/* include any libc header to get the libc defines */
-#ifdef __GLIBC__
-# undef __USE_XOPEN
-#endif
-
 #include <errno.h>
 
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #ifdef HAVE_SYS_IOCTL_H
 # include <sys/ioctl.h>
 #endif

Index: src/OFSystemInfo.m
==================================================================
--- src/OFSystemInfo.m
+++ src/OFSystemInfo.m
@@ -16,18 +16,20 @@
 
 #define __NO_EXT_QNX
 
 #include "config.h"
 
-/* Work around __block being used by glibc */
 #include <stdlib.h>	/* include any libc header to get the libc defines */
-#ifdef __GLIBC__
-# undef __USE_XOPEN
-#endif
 
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #include "platform.h"
 
 #ifdef OF_MACOS

Index: src/OFThread.m
==================================================================
--- src/OFThread.m
+++ src/OFThread.m
@@ -22,24 +22,25 @@
 
 #include <stdlib.h>
 #include <math.h>
 #include <time.h>
 
-/* Work around __block being used by glibc */
-#ifdef __GLIBC__
-# undef __USE_XOPEN
-#endif
-
-#include "platform.h"
-
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #ifdef OF_HAVE_SCHED_YIELD
 # include <sched.h>
 #endif
+
+#include "platform.h"
 
 #ifdef OF_WII
 # define BOOL OGC_BOOL
 # define nanosleep ogc_nanosleep
 # include <ogcsys.h>

Index: src/socket_helpers.h
==================================================================
--- src/socket_helpers.h
+++ src/socket_helpers.h
@@ -14,17 +14,20 @@
  * file.
  */
 
 #include "config.h"
 
-/* Work around __block being used by glibc */
-#ifdef __GLIBC__
-# undef __USE_XOPEN
-#endif
+#include <stdlib.h>	/* include any libc header to get the libc defines */
 
 #ifdef HAVE_UNISTD_H
+# ifdef __GLIBC__
+#  undef __USE_XOPEN	/* Needed to avoid old glibc using __block */
+# endif
 # include <unistd.h>
+# ifdef __GLIBC__
+#  define __USE_XOPEN 1
+# endif
 #endif
 
 #ifdef HAVE_ARPA_INET_H
 # include <arpa/inet.h>
 #endif