i386: Enable *rsqrtsf2_sse without TARGET_SSE_MATH [PR117357]

__builtin_ia32_rsqrtsf2 expander generates UNSPEC_RSQRT insn pattern
also when TARGET_SSE_MATH is not set.  Enable *rsqrtsf2_sse without
TARGET_SSE_MATH to avoid ICE with unrecognizable insn.

	PR target/117357

gcc/ChangeLog:

	* config/i386/i386.md (*rsqrtsf2_sse):
	Also enable for !TARGET_SSE_MATH.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr117357.c: New test.