[arm] Fix use of CRC32 intrinsics with Armv8-a and hard-float

[arm] Fix use of CRC32 intrinsics with Armv8-a and hard-float

We currently have a nasty error when trying to use the __crc* intrinsics
with an -mfloat-abi=hard.
That is because the target pragma guarding them uses armv8-a+crc that
does not include fp by default.
So we get errors like:
error: '-mfloat-abi=hard': selected processor lacks an FPU

This patch fixes that by using an FP-enabled arch target pragma to guard
these intrinsics when floating-point is available.
That way both the softfloat and hardfloat variants work.

     * config/arm/arm_acle.h: Use arch=armv8-a+crc+simd pragma for CRC32
     intrinsics if __ARM_FP.
     Use __ARM_FEATURE_CRC32 ifdef guard.

     * gcc.target/arm/acle/crc_hf_1.c: New test.

From-SVN: r274827