ARM thumb-interwork libgcc asm functions have no bx

[Richard Earnshaw]

Giuliano,

Can you please try the following patch.  You will need to rebuild the 
compiler and (at the very least) the interworking versions of libgcc.a

Richard.

	* arm.h (CPP_SPEC): Use sub-spec cpp_interwork.
	(CPP_INTERWORK_SPEC, CPP_INTEWORK_DEFAULT_SPC): New sub-specs.
	(EXTRA_SPECS): Add them.
	* arm/lib1funcs.asm: Support builds for interworking.