arm: Fix up arm installed unwind.h for use in pedantic modes [PR93615]

Commit r10-6500-g811a475ea3fcc55ee4aea7c81171891ef19dfc25 broke the
GCC build for arm-none-uclinuxfdpiceabi, as it forgot to update some
uses of gnu_Unwind_Find_got.

2020-02-10  Christophe Lyon  <christophe.lyon@linaro.org>

	libgcc/
	PR target/93615
	* unwind-arm-common.inc: Replace uses of gnu_Unwind_Find_got with
	_Unwind_gnu_Find_got.
	* unwind-pe.h: Likewise.