checkasm: fix default build on Haiku

Haiku atm builds executeables by defaults as shared libraries
and with checkasm_fail_func being a global symbol, but assembly
expecting to call a local symbol building was broken.

Building with -fvisibility=hidden or adding any single one of -pie,
-no-pie and -Bsymbolic to linking flags also worked around this issue.

checkasm/checkasm.c

@@ -736,6 +736,7 @@ int checkasm_bench_func(void) {
 
 /* Indicate that the current test has failed, return whether verbose printing
  * is requested. */
+ASM_CALLABLE
 int checkasm_fail_func(const char *const msg, ...) {
     if (state.current_func_ver && state.current_func_ver->cpu &&
         state.current_func_ver->ok)

checkasm/checkasm.h

@@ -335,4 +335,10 @@ void checkasm_stack_clobber(uint64_t clobber, ...);
     line __attribute__((aligned(align)))
 #endif
 
+#ifdef _MSC_VER
+#define ASM_CALLABLE
+#else
+#define ASM_CALLABLE __attribute__((visibility("hidden")))
+#endif
+
 #endif /* CHECKASM_CHECKASM_H */