re PR target/38904 (Shared libgcc DLL violates Cygwin platform conventions.)

re PR target/38904 (Shared libgcc DLL violates Cygwin platform conventions.)

	PR target/38904
	* mkmap-flat.awk (END):  Use pe_dll command-line arg to pass
	LIBRARY name in, instead of hard-coding it.
	* config.gcc (i[34567]86-*-pe | i[34567]86-*-cygwin*):  Add an
	extra target make frag to tmake_files according to EH model.
	(i[34567]86-*-mingw* | x86_64-*-mingw*):  Likewise.
	* config/i386/t-dw2-eh, config/i386/t-sjlj-eh:  Add new target
	frags that define makefile variable EH_MODEL appropriately.
	* config/i386/cygming.h (DWARF2_UNWIND_INFO):  Add comment.
	* config/i386/cygwin.h (LIBGCC_EH_EXTN):  Define to nothing or
	to "-sjlj" according to type of EH configured.
	(LIBGCC_SONAME):  Concatenate it to shared library base name.
	* config/i386/mingw32.h (LIBGCC_EH_EXTN):  Define to "_dw2" or
	to "_sjlj" according to type of EH configured.
	(LIBGCC_SONAME):  Concatenate it to shared library base name.
	* config/i386/t-cygming (SHLIB_SONAME):  Use EH_MODEL.
	(SHLIB_LINK):  Add missing semicolon to if-else construct.
	(SHLIB_MKMAP_OPTS):  Pass library name to mkmap-flat.awk as
	string value of "pe_dll" command-line option.
	* config/i386/t-cygwin (SHLIB_EH_EXTENSION):  New helper.
	(SHLIB_SONAME):  Use it when overriding t-cygming default.
	(SHLIB_IMPLIB):  Override t-cygming default.
	(SHLIB_MKMAP_OPTS):  Pass library name to mkmap-flat.awk as
	string value of "pe_dll" command-line option.

From-SVN: r143829