[Driver][Gnu] Support -shared -static: pass -shared to ld and use crtbeginS.o

This mode never works (mismatching crtbeginT.o and crtendS.o) and probably
unsupported by GCC on glibc based Linux distro (incorrect crtbeginT.o causes
linker error) but makes sense (-shared means building a shared object, -static
means avoid shared object dependencies) and can be used on musl based Linux
distro.

mingw supports this mode as well.