* gthr-gnat.c, gthr-gnat.h, gthr.h, libgcc2.h, unwind-dw2-fde.h

	* unwind.h: Surround all visibility pragmas with #ifndef HIDE_EXPORTS.

	* mklibgcc.in: Drastic restructure for comprehensibility.
	Remove the old hidden-directive hack.
	Eliminate support for .txt files in LIB2ADD etc (never used).
	Eliminate support for assembly source files in LIB2ADDEH* and
	LIBUNWIND (also never used).
	Build up dependency lists for libraries incrementally.
	If we have SHLIB_LINK, compile each file twice, once for the
	static and once for the shared library; also probe for
	-fvisibility=hidden in the generated libgcc.mk.  If found,
	pass that and -DHIDE_EXPORTS to the compilation of every C
	source file going into the static library.  If found, generate
	hidden-directive lists for every assembly source file going
	into the static library, but incorporate them with -include
	instead of ld -r.
	Write comments into generated libgcc.mk to facilitate debugging.
	* Makefile.in: Pass ASM_HIDDEN_OP to mklibgcc.
	* config/t-slibgcc-darwin: Define ASM_HIDDEN_OP.

	* config/darwin.h (REAL_LIBGCC_SPEC): Put -lgcc back in
	-Zdynamiclib case.

From-SVN: r91513