Only usable with -i, no stdout handling

[lahwaacz]

The wrapper only works when the user passes -i to clang-format to do in-place formatting. Otherwise, clang-format takes the file (where p-clang-format commented out the pragmas) and prints the formatted source to stdout. Then, p-clang-format changes the file (unmodified by clang-format) to its original state and pragmas stay commented out in the stdout.