buffer: detect compilers not supporting __VA_ARGS__

ConfigureChecks.cmake

@@ -203,6 +203,18 @@ int main(void)
     return 0;
 }" HAVE_GCC_VOLATILE_MEMORY_PROTECTION)
 
+check_c_source_compiles("
+#include <stdio.h>
+#define __VA_NARG__(...) (__VA_NARG_(_0, ## __VA_ARGS__, __RSEQ_N()) - 1)
+#define __VA_NARG_(...) __VA_ARG_N(__VA_ARGS__)
+#define __VA_ARG_N( _1, _2, _3, _4, _5, _6, _7, _8, _9,_10,N,...) N
+#define __RSEQ_N() 10, 9,  8,  7,  6,  5,  4,  3,  2,  1,  0
+#define myprintf(format, ...) printf((format), __VA_NARG__(__VA_ARGS__), __VA_ARGS__)
+int main(void) {
+    myprintf(\"%d %d %d %d\",1,2,3);
+    return 0;
+}" HAVE_GCC_NARG_MACRO)
+
 if (WITH_DEBUG_CRYPTO)
   set(DEBUG_CRYPTO 1)
 endif (WITH_DEBUG_CRYPTO)

config.h.cmake

@@ -144,6 +144,7 @@
 #cmakedefine HAVE_MSC_THREAD_LOCAL_STORAGE 1
 
 #cmakedefine HAVE_GCC_VOLATILE_MEMORY_PROTECTION 1
+#cmakedefine HAVE_GCC_NARG_MACRO 1
 
 /* Define to 1 if you want to enable GSSAPI */
 #cmakedefine WITH_GSSAPI 1