Allow bypass of Common and Language Flags

[hansenji]

I have a c library I am using that is delivered as source code and the library maintainers have unfortunately chosen to leave in some warnings that are erring out the build with the -werror flag being applied.

I would be happy to make a PR with either:

1. Making compilerFlags editable
2. Adding a excludeCommonCompilerFlags property, that would only return the compilerArgs for the compilerFlags so a user would have to supply all the flags but I think that makes a more comfortable trade off.