[sanitizer] Implement GetNumberOfCPUs for Windows

Summary:
Implement `GetNumberOfCPUs` using `GetNativeSystemInfo`.
The only consummer of this function is Scudo which is not functional on
Windows yet.

Reviewers: rnk, zturner

Reviewed By: zturner

Subscribers: zturner, kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D42547

llvm-svn: 323462

compiler-rt/lib/sanitizer_common/sanitizer_win.cc

@@ -1106,9 +1106,10 @@ bool GetRandom(void *buffer, uptr length, bool blocking) {
   UNIMPLEMENTED();
 }
 
-// FIXME: implement on this platform.
 u32 GetNumberOfCPUs() {
-  UNIMPLEMENTED();
+  SYSTEM_INFO sysinfo = {0};
+  GetNativeSystemInfo(&sysinfo);
+  return sysinfo.dwNumberOfProcessors;
 }
 
 }  // namespace __sanitizer