Mark various tests that require a c99 libm

Mark various tests that require a c99 libm

A number of i386 math optimisation tests are looking assembly instructions
that are only emitted when the compiler knows the target has a C99 libm
available. Since targets like *-elf may not have such a libm, a C99 runtime
requirement is added to these tests.

gcc/testsuite/ChangeLog

	* gcc.target/i386/387-7.c: Add dg-require-effective-target c99_runtime.
	* gcc.target/i386/387-9.c: Likewise.
	* g++.target/i386/avx512bw-pr96246-1.C: Likewise.
	* gcc.target/i386/avx512f-rint-sfix-vec-2.c: Likewise.
	* gcc.target/i386/avx512f-rintf-sfix-vec-2.c: Likewise.
	* g++.target/i386/avx512vl-pr96246-1.C: Likewise.
	* gcc.target/i386/pr61403.c: Likewise.
	* gcc.target/i386/sse4_1-ceil-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-ceilf-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-floor-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-floorf-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-rint-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-rintf-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-round-sfix-vec.c: Likewise.
	* gcc.target/i386/sse4_1-roundf-sfix-vec.c: Likewise.