clang: make atomics work

configure.ac

@@ -37,6 +37,16 @@ AC_INIT(configure.ac)
 
     if test `basename $CC` = "clang"; then
         CFLAGS="$CFLAGS -Wextra -Werror-implicit-function-declaration"
+        AC_MSG_CHECKING([clang __sync_bool_compare_and_swap])
+        AC_TRY_COMPILE([#include <stdio.h>],
+                [ unsigned int i = 0; (void)__sync_bool_compare_and_swap(&i, 1, 1);],
+                [
+                    AC_DEFINE([__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1], [1], [Fake GCC atomic support])
+                    AC_DEFINE([__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2], [1], [Fake GCC atomic support])
+                    AC_DEFINE([__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4], [1], [Fake GCC atomic support])
+                    AC_DEFINE([__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8], [1], [Fake GCC atomic support])
+                    AC_MSG_RESULT([yes]) ],
+                [AC_MSG_RESULT([no])])
     fi
     if test `basename $CC` = "gcc"; then
         dnl get gcc version