sanitizers: disable calls to pthread_atfork

OpenBLAS tries to do bad things in this callback (supposedly to support
use-after-fork), so we disable it entirely for TSAN/ASAN, where it
causes the sanitizers to deadlock.

cli/loader_exe.c

@@ -63,6 +63,15 @@ int main(int argc, char * argv[])
     return ret;
 }
 
+#if defined(_COMPILER_ASAN_ENABLED_) || defined(_COMPILER_TSAN_ENABLED_)
+// fork is generally bad news, but it is better if we prevent applications from
+// making it worse as openblas threadpools cause it to hang
+int __register_atfork232(void (*prepare)(void), void (*parent)(void), void (*child)(void), void *dso_handle) {
+    return 0;
+}
+__asm__ (".symver __register_atfork232, __register_atfork@@GLIBC_2.3.2");
+#endif
+
 #ifdef __cplusplus
 } // extern "C"
 #endif