This patch is mainly to fix a regression on trunk with support for
__ctzsi2 on cores that do not have the CLZ instruction (notably pre-v5
and cortex-m0).  It's needed after a recent change to longlong.h which
now defines count_trailing_zeros to use the GCC builtin: unfortunately
that builtin is used in the default libgcc definition of __ctzsi2 and
gcc furthermore falls back when it has no sequence to implement that
builting by calling the __ctzsi2 helper function...

The patch addresses the problem by providing suitable assembly-language
definitions that break the recursive loop.  They're also marginally
optimized over the alternative of calling __clzsi2 to provide the
implementation.

Tested on bare metal for both thumb1 and pre-v5 ARM and committed to trunk.

No need for additional tests, this fixes FAILs on the FFS2 tests.

	* arm/lib1funcs.asm (ctzsi2): New function.
	* arm/t-elf (LIB1ASMFUNCS): Add _ctzsi2.
	* arm/t-linux (LIB1ASMFUNCS): Likewise.
	* arm/t-strongarm-elf (LIB1ASMFUNCS): Likewise.
	* arm/t-symbian (LIB1ASMFUNCS): Likewise.
	* arm/t-vxworks (LIB1ASMFUNCS): Likewise.
	* arm/t-wince-pe (LIB1ASMFUNCS): Likewise.

R.