[libfuzzer] Prevent MSan false positive when printing log with -jobs (llvm#91679)

libfuzzer's -jobs option will, depending on the number of CPUs, spin up
a
WorkerThread and end up printing the log file using CopyFileToErr.
This leads to an MSan false positive. This patch disables the MSan
interceptor checks,
similarly to other instances in https://reviews.llvm.org/D48891

Side-note: this false positive issue first appeared when printf()
was replaced by puts() (90b4d1b).
The interceptor check was always present; however, MSan does not
check_printf by default.

Author: thurstond

compiler-rt/lib/fuzzer/FuzzerDriver.cpp

@@ -229,6 +229,7 @@ static void PulseThread() {
 
 static void WorkerThread(const Command &BaseCmd, std::atomic<unsigned> *Counter,
                          unsigned NumJobs, std::atomic<bool> *HasErrors) {
+  ScopedDisableMsanInterceptorChecks S;
   while (true) {
     unsigned C = (*Counter)++;
     if (C >= NumJobs) break;