[ubsan-minimal] Fix the ubsan_minimal debug build (COMPILER_RT_DEBUG=1) on macOS

[delcypher]

Summary

[ubsan-minimal] Fix the ubsan_minimal debug build (COMPILER_RT_DEBUG=1) on macOS.

ubsan_minimal makes use of the _sanitizer::atomic_load function.
This function uses the DCHECK macro which in debug builds will use
the _sanitizer::CheckFailed function.

This function is part of sanitizer_common but ubsan_minimal doesn't
use this so the implementation is missing which leads to link failures
on macOS when trying to link libclang_rt.ubsan_minimal_osx_dynamic.dylib.
This is in contrast to the BFD linker on Linux which doesn't seem to care
about the missing symbol.

A basic implementation of _sanitizer::CheckFailed has been added to
the ubsan_minimal debug build to avoid the link error. The
implementation could definitely be improved but I don't know which
functions can be used in this context so I decided to restrict myself to
functions only being used in ubsan_minimal already.

[delcypher]

@eugenis Thanks for approving. I'll wait a bit longer before committing as @vsk and @kubamracek might have opinions on this.

[vsk]

Thanks!

lib/ubsan_minimal/ubsan_minimal_handlers.cc

68

Could you omit the parameter names for the unused arguments? This should appease some picky buildbots.

[kubamracek]

Thanks!

[delcypher]

Remove names of unused arguments.

[delcypher]

lib/ubsan_minimal/ubsan_minimal_handlers.cc

68

Done.

The fact that this wasn't caught before though probably means we are missing a build bot configuration for macOS.

[delcypher]

Committed in r326032

lib/ubsan_minimal/ubsan_minimal_handlers.cc

 static void abort_with_message(const char *msg) {
   if (&android_set_abort_message) android_set_abort_message(msg);
   abort();
 }
 #else
 static void abort_with_message(const char *) { abort(); }
 #endif
 
+#if SANITIZER_DEBUG
+namespace __sanitizer {
+// The DCHECK macro needs this symbol to be defined.
+void NORETURN CheckFailed(const char *file, int, const char *cond, u64, u64) {
+  message("Sanitizer CHECK failed: ");
+  message(file);
+  message(":?? : "); // FIXME: Show line number.
+  message(cond);
+  abort();
+}
+} // namespace __sanitizer
+#endif
+
 #define INTERFACE extern "C" __attribute__((visibility("default")))
 
 // FIXME: add caller pc to the error message (possibly as "ubsan: error-type
 // @1234ABCD").
 #define HANDLER_RECOVER(name, msg)                               \
   INTERFACE void __ubsan_handle_##name##_minimal() {             \
     if (!report_this_error(__builtin_return_address(0))) return; \
     message("ubsan: " msg "\n");                                 \