Add miscfuncs.h to files as needed throughout.

* mount.cc: New file.
* path.cc: Move mount-specific stuff into mount.cc.  Move common stuff into
miscfuncs.cc.  Remove unneeded includes.
* miscfuncs.cc: Move some common path functions here.
* miscfuncs.h: New file.
* winsup.h: Move miscelleneous functions to miscfuncs.h.
* dcrt0.cc: Remove unneeded includes.
* Makefile.in (DLL_OFILES): Add mount.o.
* include/cygwin/config.h: Fix a minor typo.

winsup/cygwin/exceptions.cc

@@ -10,6 +10,7 @@ Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
 #include "winsup.h"
+#include "miscfuncs.h"
 #include <wingdi.h>
 #include <winuser.h>
 #include <imagehlp.h>