Bazel client, Windows/MSVC: fix path handling bugs

Fix blaze_util_windows.ConvertPath: in the MSVC
version this is using the actual %PATH% value, we
don't need to convert it.

Fix blaze_util_windows.PathAsJvmFlag: shorten the
path so we can pass it to the JVM process (long
paths aren't understood by the shell), but also
converrt backslashes to forward slashes so the JVM
won't believe we are passing paths with escaped
characters.

See #2107
See #2181

--
PiperOrigin-RevId: 149396971
MOS_MIGRATED_REVID=149396971

src/main/cpp/blaze_util_windows.cc

@@ -799,12 +799,15 @@ void ExecuteProgram(const string& exe, const std::vector<string>& args_vector) {
 string ListSeparator() { return ";"; }
 
 string PathAsJvmFlag(const string& path) {
+  string spath;
+  if (!blaze_util::AsShortWindowsPath(path, &spath)) {
+    pdie(255, "PathAsJvmFlag(%s): AsShortWindowsPath failed", path.c_str());
+  }
   // Convert backslashes to forward slashes, in order to avoid the JVM parsing
   // Windows paths as if they contained escaped characters.
   // See https://github.com/bazelbuild/bazel/issues/2576
-  string result(path);
-  std::replace(result.begin(), result.end(), '\\', '/');
-  return result;
+  std::replace(spath.begin(), spath.end(), '\\', '/');
+  return spath;
 }
 
 string ConvertPath(const string& path) {
@@ -828,6 +831,11 @@ string ConvertPath(const string& path) {
 
 // Convert a Unix path list to Windows path list
 string ConvertPathList(const string& path_list) {
+#ifdef COMPILER_MSVC
+  // In the MSVC version we use the actual %PATH% value which is separated by
+  // ";" and contains Windows paths.
+  return path_list;
+#else   // not COMPILER_MSVC
   string w_list = "";
   int start = 0;
   int pos;
@@ -839,6 +847,7 @@ string ConvertPathList(const string& path_list) {
     w_list += ConvertPath(path_list.substr(start));
   }
   return w_list;
+#endif  // COMPILER_MSVC
 }
 
 static string ConvertPathToPosix(const string& win_path) {