testsuite/arm: Fix and rename arm_qbit_ok into arm_sat_ok effective-target

The acle/saturation.c test uses __[su]sat() and
__saturation_occurred() intrinsics but __[su]sat() are defined in
acle.h if __ARM_FEATURE_SAT true, while __saturation_occurred()
depends on __ARM_FEATURE_QBIT.

QBIT is a v5te feature, while SAT is available since v6, so the test
really needs __ARM_FEATURE_SAT, to have both available.

This patch renames arm_qbit_ok into arm_sat_ok and checks
__ARM_FEATURE_SAT. It updates acle/saturation.c accordingly.

This enables the test to pass on arm-eabi with default cpu/fpu/mode,
where arm_qbit previously used -march=armv5te instead of armv6 now.

2021-05-17  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* doc/sourcebuild.texi (arm_qbit_ok): Rename into...
	(arm_sat_ok): ...this.

	gcc/testsuite/
	* gcc.target/arm/acle/saturation.c: Use arm_sat_ok effective
	target.
	* lib/target-supports.exp
	(check_effective_target_arm_qbit_ok_nocache): Rename into...
	(check_effective_target_arm_sat_ok_nocache): ... this. Check
	__ARM_FEATURE_SAT and use armv6.