Do not allow divide-by-zero exception for pow(+/- 0, -Inf).

Do not allow divide-by-zero exception for pow(+/- 0, -Inf).

C99 wrongly specified a divide-by-zero exception for pow(+/- 0, -Inf);
C11 made it optional after this was pointed out, and the permission
for this exception has been removed in the current C2x draft.  This
patch makes the glibc pow tests reflect the stricter requirement
(which follows the normal IEEE rules that a divide-by-zero exception
is for the case of exact infinite results from *finite* operands, not
for such results when any operand is infinite).

Tested for x86_64 and x86.  (If any other pow implementation in glibc,
not exercised on those architectures, turns out to fail the stricter
test, it should be fixed to avoid the exception in this case.)

	* math/libm-test-pow.inc (pow_test_data): Do not allow
	divide-by-zero exception for pow(+/- 0, -Inf).