Fail loudly when clang-format is unavailable
Fail loudly when clang-format is unavailable

Without this change, if clang-format is not available for the current
platform (e.g. android_x64), running this tool has no output and exits
with status 0. If clang-format is used to filter files, it would
effectively empty the file.

After this change, clang-format will fail with status 1 and an error
message to stderr.

angular/clang-format,angular/clang-format,angular/clang-format