[test][asan] Fix test on MacOS 12+

[rsundahl]

LGTM. Could limit it to just Apple but shouldn't matter. Thank you.

compiler-rt/test/asan/TestCases/report_error_summary.cpp

10

We generally are using the pattern:

// Required for dyld macOS 12.0+
#if (__APPLE__)
__attribute__((weak))
#endif

at this line but this will work just as well.

compiler-rt/test/asan/TestCases/report_error_summary.cpp

 // RUN: %clangxx_asan -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 // FIXME: Doesn't work with DLLs
 // XFAIL: win32-dynamic-asan
 
 #include <stdio.h>
 
+// Required for ld64 macOS 12.0+
+__attribute__((weak)) extern "C" void foo() {}
+
 extern "C" void __sanitizer_report_error_summary(const char *summary) {
   fprintf(stderr, "test_report_error_summary\n");
   // CHECK: test_report_error_summary
   fflush(stderr);
 }
 
 char *x;
 
 int main() {
   x = new char[20];
   delete[] x;
   return x[0];
 }