Fix build_init vcxproj to correctly detect changes in config.h.

Fix build_init vcxproj to correctly detect changes in config.h.

build_init project doesn't detect changes done in config.h. This is needed in order
for build_init to replace config.h with winconfig.h and backup cygconfig.h. This is
normally an issue if you do a reconfigure and build using make and then msbuild. The msbuild
will then fail, since config.h is still the cygwin version. Solution is to do a rebuild all
that will trigger build_init. This fix will make sure that build_init gets invoked if there has been a change to config.h.

There was also a very old issue with the first copy of config.h -> cygconfig.h. This is only done
if there is no cygconfig.h in the directory. This means that the cygconfig.h will not be update until
deleted and a new build_init has been invoked. This fix will make sure cygconfig.h is always updated
if config.h is the cygwin generated version (not already replaced with winconfig.h).