Split -Wmicrosoft into many specific warnings.

Also move "pragma comment" warning from -Wmicrosoft to -Wignored-pragmas.

-Wmicrosoft currently covers many different areas, some more useful than
others.  Split it into many targeted flags, so that projects can choose to
enable only a subset of these warnings.  This is also useful for incrementally
fixing and turning on these warnings.

-Wno-microsoft still disables all these warnings, and -Wmicrosoft still enables
them all.  After this change, it's possible to pass `-Wno-microsoft
-Wmicrosoft-unqualified-friend` to only enable -Wmicrosoft-unqualified-friend,
and `-Wmicrosoft -Wno-microsoft-unqualified-friend` to enable all other
Microsoft warnings.

I put all the template-related warnings behind -Wmicrosoft-template; if that
turns out to be too coarse we can make that finer later on. (In practice, I
haven't seen the template-related warnings fire frequently.)

Reviewed at http://reviews.llvm.org/D11504

llvm-svn: 243371