[libFuzzer] Implement TmpDir() for Windows.

[amccarth]

lib/Fuzzer/FuzzerIOWindows.cpp

291

Consider using GetTempPath, which starts by looking at the TMP environment variable, but will also check for a temp directory setting in several other places.

https://msdn.microsoft.com/en-us/library/windows/desktop/aa364992(v=vs.85).aspx

[mpividori]

@amccarth Thanks for your comment. Let me know if you agree with this new diff.

[amccarth]

LGTM.

lib/Fuzzer/FuzzerIOWindows.cpp

if (!LocationLen) { // Relative path.
     if (!DirLen)
       return ".";
     return std::string(".\\").append(FileName, 0, DirLen);
   }
 
   return FileName.substr(0, LocationLen + DirLen);
 }
 
-std::string TmpDir() { return "TODO: implement TmpDir"; }
+std::string TmpDir() {
+  if (auto Env = getenv("TMP"))
+    return Env;
+  Printf("Couldn't read TMP environment variable\n");
+  exit(1);
+}
 
 bool IsInterestingCoverageFile(const std::string &FileName) {
   if (FileName.find("Program Files") != std::string::npos)
     return false;
   if (FileName.find("compiler-rt\\lib\\") != std::string::npos)
     return false; // sanitizer internal.
   if (FileName == "<null>")
     return false;
   return true;
 }
 
 }  // namespace fuzzer
 
 #endif // LIBFUZZER_WINDOWS