Add -mno-cygwin flag that links in the mingw libraries.

Add -mno-cygwin flag that links in the mingw libraries.
	* i386/cygwin32.h (MASK_WIN32, MASK_CYGWIN, MASK_WINDOWS, MASK_DLL,
	TARGET_WIN32, TARGET_CYGWIN, TARGET_WINDOWS, TARGET_DLL): New.
	(SUBTARGET_SWITCHES): Add -mno-cygwin, -mcygwin, and -mdll options.
	(CPP_PREDEFINES): Don't define __CYGWIN32__ here.
	(STARTFILE_SPEC): Handle -mdll, -mno-cygwin options.
	(CPP_SPEC): Handle -mno-cygwin option.  Define __CYWIN__ in addition
	to __CYGWIN32__.
	(LIB_SPEC): Handle -mno-cyginw option.
	(LINK_SPEC): Handle -mdll.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@23523 138bc75d-0d04-0410-961f-82ee72b054a4