[Compiler-RT] Remove FlushViewOfFile call when unmapping gcda files on win32.

[Abpostelnicu]

Summary

This patch was pushed for [e-mail]

• this function (Windows only) is called when gcda are dumped on disk;
• according to its documentation, it's only useful in case of hard failures, this is highly improbable;
• it drastically decreases the time in the tests and consequently it avoids timeouts when we use slow disks.

[calixte]

This patch is running for months in Firefox's CI and we didn't observe anything wrong and thanks to it we fixed several timeout issues.
I suppose that in case of hard failures, the partial ccov data are likely useless and everything will be ran again.

compiler-rt/lib/profile/GCDAProfiling.c

 /*===- GCDAProfiling.c - Support library for GCDA file emission -----------===*\
 |*
 |* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 |* See https://llvm.org/LICENSE.txt for license information.
 |* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-|* 
+|*
 |*===----------------------------------------------------------------------===*|
-|* 
+|*
 |* This file implements the call back routines for the gcov profiling
 |* instrumentation pass. Link against this library when running code through
 |* the -insert-gcov-profiling LLVM pass.
 |*
 |* We emit files in a corrupt version of GCOV's "gcda" file format. These files
 |* are only close enough that LCOV will happily parse them. Anything that lcov
 |* ignores is missing.
 |*

 
 /*
  * The current file name we're outputting. Used primarily for error logging.
  */
 static char *filename = NULL;
 
 /*
  * The current file we're outputting.
- */ 
+ */
 static FILE *output_file = NULL;
 
 /*
  * Buffer that we write things into.
  */
 #define WRITE_BUFFER_SIZE (128 * 1024)
 static unsigned char *write_buffer = NULL;
 static uint64_t cur_buffer_size = 0;
#else
   }
 #endif
 
   return 0;
 }
 
 static void unmap_file() {
 #if defined(_WIN32)
-  if (!FlushViewOfFile(write_buffer, file_size)) {
-    fprintf(stderr, "profiling: %s: cannot flush mapped view: %lu\n", filename,
-            GetLastError());
-  }
-
   if (!UnmapViewOfFile(write_buffer)) {
     fprintf(stderr, "profiling: %s: cannot unmap mapped view: %lu\n", filename,
             GetLastError());
   }
 
   if (!CloseHandle(mmap_handle)) {
     fprintf(stderr, "profiling: %s: cannot close file mapping handle: %lu\n",
             filename, GetLastError());