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.
From-SVN: r23523