Extract compiler-specific macro definitions in a new wx/compiler.h.

This solves the problem with wx/defs.h -> wx/platform.h -> wx/setup.h which
resolves to msvc/wx/setup.h -> wx/version.h -> wx/cpp.h include path which
resulted in __VISUALC__ not being defined in wx/cpp.h.

This problem was not new but went unnoticed for a long time and was only
discovered when wxCHECK_VISUALC_VERSION() started being used in wx/cpp.h too
as now the compiler started warning about wrong #if syntax due to it being
undefined.

Putting the compiler-specific definitions in a separate file allows this file
to be included from wx/cpp.h to ensure that these symbols are always defined
in it and also makes things a little better organized.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74496 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Rebake all the samples and others makefiles too.

The samples makefiles were not regenerated after the recent Scintilla changes
(see r74425), do it now. There are no real changes for most of them (except
stc sample), but it ensures that rerunning bakefile doesn't change anything.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74497 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775