Add demangle option to omit vendor-specific suffixes

[leftmostcat]

It doesn't currently seem to be possible to automatically compare two symbols without regard to e.g. clone suffixes, which are a part of the vendor-specific suffix section. It should be possible to demangle in such a way that a simple matching comparison between the results of demangling _ZL8fit_lineP9lsfit_acciPiS1_P18vorbis_info_floor1.isra.2 and _ZL8fit_lineP9lsfit_acciPiS1_P18vorbis_info_floor1 is possible.