Support for gcc -wrapper option about ccache

[jrosdahl]

Not sure if it's possible to support -wrapper in a reasonable way, but here are some notes for a potential implementation:

• Need to handle -wrapper @file specially where the @file part does not get expanded like normal @file arguments do.
• Need to split the argument to -wrapper on , to find the wrapper executable.
• Probably should run hash_compiler on the wrapper executable. This should be enough for things like running strace or gdb, but is it enough for wrappers that modify the outcome?

Meanwhile I'll mark -wrapper as "too hard" so that the result will be "unsupported compiler option" instead of "multiple source files".