Disable MSVC warning C4986

This is a new warning in Visual Studio 2012.

Otherwise, when using /Wall (as we do), you get tons of warnings from
the compiler's own headers:

.../crtdbg.h(1041) : warning C4986: 'operator new[]': exception
  specification does not match previous declaration
.../new(79) : see declaration of 'operator new[]'

It seems to be generally recommended not to use /Wall with MSVC (that
option does not really have the same intended use as gcc's -Wall,
people say), but use /W4 instead:
http://stackoverflow.com/a/4001759/259398

So maybe we should change that -Wall to -W4?

Also, we should go over the long list of -wd options and check each
whether we really want it or not. Maybe, while at it, add a comment
for each giving its one-line meaning.

solenv/gbuild/platform/com_MSC_defs.mk

@@ -184,6 +184,20 @@ gb_CXXFLAGS := \
 	-Zc:forScope,wchar_t- \
 	-Zm500 \
 
+# New warning(s) in Visual Studio 2012, let's try disabling these only
+# for that specific compiler version, in case a later one will not
+# need them disabled.
+ifeq ($(VCVER),110)
+
+# C4986: 'function': exception specification does not match previous
+#   declaration. This warning is generated by VS2012 headers (!), and is
+#   C++-only.
+
+gb_CXXFLAGS += \
+	-wd4986 \
+
+endif
+
 gb_STDLIBS := \
 	advapi32.lib \