cc: Only enable ARM_NEON when in target_feature

[wcampbell0x2a]

• Fix armv7-unknown-linux-musleabi and arm-unknown-linux-musleabi by only passing in ARM_NEON if that target is enabled.
• This was only tested without neon, and not tested with neon support

To enable NEON in the future, I think the following will need to be addressed with adding compiler options:

  cargo:warning=                 from src/zlib-ng/arch/arm/slide_hash_neon.c:12:
  cargo:warning=/usr/local/lib/gcc/arm-linux-musleabi/9.2.0/include/arm_neon.h:31:2: error: #error "NEON intrinsics not available with the soft-float ABI.  Please use -mfloat-abi=softfp or -mfloat-abi=hard"
  cargo:warning=   31 | #error "NEON intrinsics not available with the soft-float ABI.  Please use -mfloat-abi=softfp or -mfloat-abi=hard"

[Byron]

Thanks a lot!