This allows non-msys build systems to use the triplet prefixed
compiler frontends on windows.
Keep the old shell script version as well, for easier hackability
on unix platforms.
This avoids needing the clang++ symlink. On platforms without symlinks
(i.e. windows), clang.exe and clang++.exe are two separate but identical
executables. This allows getting rid of the latter, saving size.
Provide wrappers named <triplet>-gcc and <triplet>-g++ as well,
to ease cross compilation with e.g. autotools, to allow just
specifying --host=<triplet>.
Provide wrappers for objdump and ld that provide specific output
that autotools look for.
Provide <triplet>-strip as a symlink to /bin/true, since there is
no strip tool available yet (and llvm-objcopy doesn't support
COFF yet).