Initial attempt at fixing use of -arch, -m32, and -march in combination.
Revert "Initial attempt at fixing use of -arch, -m32, and -march in combination."

This reverts commit b5d958d8d42483da8a5efd85c9f86f50380df938.
Implement better -m(32|64)/-march/-mcpu handling.

After being fully populated, the compiler's arguments are scanned for
existing architecture flags, and the default flags are only added if
they will not override an existing flag.
Add support for marking flags that are only compatible when using -Xarch_*
Add missing '-specs' argument entry.