InstallRequiredSystemLibraries: MBCS MFC is optional on VS 12 (#14903)

The MBCS (Multi-Byte Character Set) has been deprecated with VS 2013,
and MSVC no longer ships with an MBCS-version of MFC by default.
However, it can be downloaded as an add-on.

Teach InstallRequiredSystemLibraries to install the MBCS MFC only
for VS < 12 or if it happens to exist on the system.
Merge branch 'InstallRequiredSystemLibraries-vs12-mfc' into release
KWSys SystemInformation: Include backtrace APIs whenever we use them

Include execinfo.h, cxxabi.h, and dlfcn.h under the same conditions
under which we use the APIs from them.  Move their inclusion out of
OS-specific blocks.
Merge branch 'backport-kwsys-compile-fix' into release
CompileFlags: Test for C++ features after selecting flags

Some flags we select may affect availability of C++ features.
CompileFlags: Add -AA +hpxstd98 on HP-UX 11.11 with aCC

These flags are needed to enable support for C++98.  Also teach the
'bootstrap' script to add them if necessary.
CompileFlags: add better selection which aCC version gets -AA +hpxstd98 flags
Merge branch 'hpux-compile' into release