Remove a couple of memset usages from TSan, introduced in r288624.

[sammccall]

Summary

TSan runtime shouldn't contain memset, so internal_memset is used instead and
syntax that emits memset is avoided.

This doesn't fail in-tree due to TSan being build with -03, but it fails
when TSan is built with -O0, and is (I think) a true positive.

[dvyukov]

LGTM

[djasper]

Submitted as r288672.

[kubamracek]

Do we have a way to catch this? Something I should have done before submitting this change?

[kubamracek]

Also, why don't we build with -ffreestanding? Shouldn't that prevent all such calls?

[dvyukov]

You need to reconfigure with -DCOMPILER_RT_DEBUG=ON to get -O0 build.
There is no way to stop llvm from emitting calls to memset/memcpy. -ffreestanding does not help.

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

if (!reported_invalid_path_) {
       Report("WARNING: invalid path to external symbolizer!\n");
       reported_invalid_path_ = true;
     }
     return false;
   }
 
   int pid = -1;
 
-  int infd[2] = {};
-  int outfd[2] = {};
+  int infd[2];
+  internal_memset(&infd, 0, sizeof(infd));
+  int outfd[2];
+  internal_memset(&outfd, 0, sizeof(outfd));
   if (!CreateTwoHighNumberedPipes(infd, outfd)) {
     Report("WARNING: Can't create a socket pair to start "
            "external symbolizer (errno: %d)\n", errno);
     return false;
   }
 
   if (use_forkpty_) {
 #if SANITIZER_MAC