sanitizer_common: tighten on_print hook test

[dvyukov]

Summary

The new tsan runtime does not support arbitrary forms
of recursing into the runtime from hooks.
Disable instrumentation of the hook and use write instead
of fwrite (calls malloc internally).
The new version still recurses (write is intercepted),
but does not fail now (the issue at hand was malloc).

Depends on D112601.

compiler-rt/test/sanitizer_common/TestCases/onprint.cpp

 // Checks that the __sanitizer_on_print hook gets the exact same sanitizer
 // report as what is printed to stderr.
 //
 // RUN: %clangxx %s -o %t
 // RUN: %run %t %t-onprint.txt 2>%t-stderr.txt || true
 // RUN: diff %t-onprint.txt %t-stderr.txt
 //
 // UNSUPPORTED: android
 
 #include <cassert>
-#include <cstdio>
 #include <cstdlib>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
 
-FILE *f;
+int f;
 volatile void *buf;
 volatile char sink;
 
-extern "C" void __sanitizer_on_print(const char *str) {
-  fprintf(f, "%s", str);
-  fflush(f);
+__attribute__((disable_sanitizer_instrumentation)) extern "C" void
+__sanitizer_on_print(const char *str) {
+  write(f, str, strlen(str));
 }
 
 int main(int argc, char *argv[]) {
   assert(argc >= 2);
-  f = fopen(argv[1], "w");
+  f = open(argv[1], O_WRONLY);
 
   // Use-after-free to trigger ASan/TSan reports.
   void *ptr = malloc(1);
   buf = ptr;
   free(ptr);
   sink = *static_cast<char *>(ptr);
   return 0;
 }