Serious overhaul of the C compiler interface and the two classes that
implement it (so far):
* moved filename generation methods into CCompiler base class,
driven by data supplied by implementation classes
* moved a bunch of common code from UnixCCompiler to convenience
methods in CCompiler
* overhauled MSVCCompiler's compile/link methods to look and act
as much as possible like UnixCCompiler's, in order to regularize
both interface and behaviour (especially by using those new
convenience methods)