[ANN] --enable-dbgutil: everyone gets a Debug STL!

[Michael Stahl]

--enable-dgbutil just got better on non-mainstream platforms:

with commit f14f7a2e4568e3e85a0c8860beebd0376c5a8b51 MSVC builds will
link everything against the debug runtimes (MSVCRTD etc.), which enables
debug STL and other things.

with commit a5a5104cae175f6b9a8cb4bbaccb69f0276783e3 MacOSX build define
_GLIBCXX_DEBUG (like Linux/BSD/Android builds have done for years(,
which enables debug STL.

both of these debug modes are _NOT_ binary compatible with the non-debug
mode (which is why you have to use --enable-dbgutil to get these).

this means that if you have a --enable-dbgutil build on MacOSX or MSVC
platforms you _must_ run

                           "make clean"

when you "git pull" across these commits.

the MSVC one is tested on MSVC 2008 only, where "make check" passes
successfully; it's possible that i've overlooked something in the
makefiles where different MSVC versions use different rules, so it needs
somebody to try it out in an --enable-dbgutil build with 2010 and 2012.

since we have this enabled on other GCC platforms for years i'm not much
concerned about breakage on MacOSX; it would be helpful though if
somebody could try what happens when you run the "subsequentcheck" tests
which apparently isn't possible over SSH.