RFR: 8218164: Improve local control of compiler warnings

[Kim Barrett]

Please review this extension to the existing support for locally
disabling various compiler warnings.  There are also a few updates of
existing code to use the new mechanisms.  (There are some additional
opportunities to use these new mechanisms, but some were in code that
Oracle doesn't test, like Win32, so I left them alone.)

(Obviously one should not disable warnings lightly, but sometimes one
does what one must.)

There are several pieces to this change.

First, utilities/compilerWarnings.hpp is refactored to have
compiler-specific variants, similar to globalDefinitions.hpp.  This
hadn't been done previously because only gcc (and clang) had
non-trivial definitions.

Second, implemented PRAGMA_DIAG_PUSH/POP for Visual Studio.  Still no
implementations for xlc or solstudio though.

Third, added a couple of compiler-specific warning disabling macros:

PRAGMA_DISABLE_GCC_WARNING(option_string)  // also applies to clang
PRAGMA_DISABLE_MSVCPP_WARNING(num)

They have useful implementations for the respective compilers and
empty definitions otherwise.

(I'm open to suggestions for better names, esp. for "MSVCPP".)

CR:
https://bugs.openjdk.java.net/browse/JDK-8218164

Webrev:
http://cr.openjdk.java.net/~kbarrett/8218164/open.00/

Testing:
mach5 tier1