[libc] add cpu feature flags for SVE/SVE2/MOPS (#166884)
Add in SVE/SVE2/MOPS features for aarch64 cpus. These features may be
interesting for future memory/math routines.
SVE/SVE2 are now being accepted in more implementations:
```
❯ echo | clang-21 -dM -E - -march=native | grep -i ARM_FEAT
#define __ARM_FEATURE_ATOMICS 1
#define __ARM_FEATURE_BF16 1
#define __ARM_FEATURE_BF16_SCALAR_ARITHMETIC 1
#define __ARM_FEATURE_BF16_VECTOR_ARITHMETIC 1
#define __ARM_FEATURE_BTI 1
#define __ARM_FEATURE_CLZ 1
#define __ARM_FEATURE_COMPLEX 1
#define __ARM_FEATURE_CRC32 1
#define __ARM_FEATURE_DIRECTED_ROUNDING 1
#define __ARM_FEATURE_DIV 1
#define __ARM_FEATURE_DOTPROD 1
#define __ARM_FEATURE_FMA 1
#define __ARM_FEATURE_FP16_SCALAR_ARITHMETIC 1
#define __ARM_FEATURE_FP16_VECTOR_ARITHMETIC 1
#define __ARM_FEATURE_FRINT 1
#define __ARM_FEATURE_IDIV 1
#define __ARM_FEATURE_JCVT 1
#define __ARM_FEATURE_LDREX 0xF
#define __ARM_FEATURE_MATMUL_INT8 1
#define __ARM_FEATURE_NUMERIC_MAXMIN 1
#define __ARM_FEATURE_PAUTH 1
#define __ARM_FEATURE_QRDMX 1
#define __ARM_FEATURE_RCPC 1
#define __ARM_FEATURE_SVE 1
#define __ARM_FEATURE_SVE2 1
#define __ARM_FEATURE_SVE_BF16 1
#define __ARM_FEATURE_SVE_MATMUL_INT8 1
#define __ARM_FEATURE_SVE_VECTOR_OPERATORS 2
#define __ARM_FEATURE_UNALIGNED 1
```
MOPS is another set of extension for string operations, but may not be
generally available for now:
```
❯ echo | clang-21 -dM -E - -march=armv9.2a+mops | grep -i MOPS
#define __ARM_FEATURE_MOPS 1
```
