fix clang define __gnuc__

include/bctoolbox/tester.h

@@ -178,10 +178,15 @@ BCTBX_PUBLIC int bc_assert_va(const char *file, int line, int predicate, const c
 		bc_assert(__FILE__, __LINE__, pred, format);                                                                   \
 	} while (0)
 
+// Test if __VA_OPT__ is defined
+#define PP_THIRD_ARG(a, b, c, ...) c
+#define VA_OPT_SUPPORTED_I(...) PP_THIRD_ARG(__VA_OPT__(, ), true, false, )
+#define VA_OPT_SUPPORTED VA_OPT_SUPPORTED_I(?)
+
 #define BC_PASS(msg) bc_assert(__FILE__, __LINE__, TRUE, "BC_PASS(" #msg ").")
 #define BC_FAIL(msg) bc_assert(__FILE__, __LINE__, FALSE, "BC_FAIL(" #msg ").")
 #define BC_ASSERT(value) bc_assert(__FILE__, __LINE__, (value), #value)
-#ifdef __GNUC__ // __VA_OPT__ only in gnu c or c++20
+#if VA_OPT_SUPPORTED // __VA_OPT__ only in gnu c or c++20
 #define BC_ASSERT_MSG(value, msg, ...) bc_assert_va(__FILE__, __LINE__, (value), msg __VA_OPT__(, ) __VA_ARGS__)
 #else
 #define BC_ASSERT_MSG(value, msg, ...) bc_assert(__FILE__, __LINE__, (value), msg)