testsuite: arm: fix arm_v8_vfp_ok effective-target

testsuite: arm: fix arm_v8_vfp_ok effective-target

This effective-target does not need to check for arm32, but needs to
force -march=armv8-a, otherwise -mfpu=fp-armv8 has no useful meaning.

While fixing that, introduce
check_effective_target_arm_v8_vfp_ok_nocache, so that arm_v8_vfp_ok
behaves like arm_v8_neon_ok and many other effective-targets.

Without this patch, gcc.target/arm/attr-neon.c fails with a toolchain
configured with --with-mode=thumb --with-cpu=cortex-m0
--with-float=soft because arm_v8_vfp returns "" because arm32 is
false.  As a result, the testcase is compiled with the options needed
for arm_neon_ok, which generates an extra ".fpu neon" directive
compared to what is expected.

The patch removes -march=armv8-a from dg-options in lceil-vcvt_1.c,
lfloor-vcvt_1.c lround-vcvt_1.c and vrinta-ce.c, because this could
override what arm_v8_vfp_ok detected (and lead to 'error: selected
architecture lacks an FPU').

With this patch, the test passes, and several others are enabled:
gcc.target/arm/lceil-vcvt_1.c
gcc.target/arm/lfloor-vcvt_1.c
gcc.target/arm/lround-vcvt_1.c
gcc.target/arm/pr69135_1.c
gcc.target/arm/vmaxnmdf.c
gcc.target/arm/vmaxnmsf.c
gcc.target/arm/vminnmdf.c
gcc.target/arm/vminnmsf.c
gcc.target/arm/vrinta-ce.c
gcc.target/arm/vrintaf32.c
gcc.target/arm/vrintaf64.c
gcc.target/arm/vrintmf32.c
gcc.target/arm/vrintmf64.c
gcc.target/arm/vrintpf32.c
gcc.target/arm/vrintpf64.c
gcc.target/arm/vrintrf32.c
gcc.target/arm/vrintrf64.c
gcc.target/arm/vrintxf32.c
gcc.target/arm/vrintxf64.c
gcc.target/arm/vrintzf32.c
gcc.target/arm/vrintzf64.c
gcc.target/arm/vseleqdf.c
gcc.target/arm/vseleqsf.c
gcc.target/arm/vselgedf.c
gcc.target/arm/vselgesf.c
gcc.target/arm/vselgtdf.c
gcc.target/arm/vselgtsf.c
gcc.target/arm/vselledf.c
gcc.target/arm/vsellesf.c
gcc.target/arm/vselltdf.c
gcc.target/arm/vselltsf.c
gcc.target/arm/vselnedf.c
gcc.target/arm/vselnesf.c
gcc.target/arm/vselvcdf.c
gcc.target/arm/vselvcsf.c
gcc.target/arm/vselvsdf.c
gcc.target/arm/vselvssf.c

gcc/testsuite/ChangeLog:
	* lib/target-supports.exp
	(check_effective_target_arm_v8_vfp_ok_nocache): New.
	(check_effective_target_arm_v8_vfp_ok): Call the above helper, and
	use global flags.
	(add_options_for_arm_v8_vfp): Use et_arm_v8_vfp_flags.
	* gcc.target/arm/lceil-vcvt_1.c: Remove -march=armv8-a.
	* gcc.target/arm/lfloor-vcvt_1.c: Likewise.
	* gcc.target/arm/lround-vcvt_1.c: Likewise.
	* gcc.target/arm/vrinta-ce.c: Likewise.