libstdc++: Avoid conflicting declaration in eh_call.cc [PR112997]

r14-1527-g2415024e0f81f8 changed the parameter of the
__cxa_call_terminate definition, but there's also a declaration in
unwind-cxx.h which should have been changed too.

libstdc++-v3/ChangeLog:

	PR libstdc++/112997
	* libsupc++/unwind-cxx.h (__cxa_call_terminate): Change first
	parameter to void*.