Add depmode=msvcmsys for Microsoft Visual C++ on MSYS. * lib/depcomp [msvisualcpp]: Fork fewer processes. Filter out libtool in the preprocessor invocation (as is done in depmode=cpp). Silence compiler stderr. [msvcmsys]: New depmode as a derivative of depmode=msvisualcpp. msvcmsys transforms any backslashes into forward slashes to make the grep in depend.m4 match, instead of the "cygpath -u" that is used in msvisualcpp. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>