[Clang][ARM][Sema] Check validity of ldrexd/strexd builtin calls (#164919)

This change enables validation checks against the following two ARM
atomic builtins:
```
__builtin_arm_ldrexd
__builtin_arm_strexd
```

Previously, no checks existed for these builtins, so under a release
compiler, it would be possible to emit `ldrexd`/`strexd` under ARM
targets which set the LDREX mask (returned via `getARMLDREXMask`) to
signify these as unsupported instructions.

For example, the following would compile with errors:
```c
> type atomics.c
long long func(void) {
    long long num = 0;
    __builtin_arm_strex(42, &num);
    return __builtin_arm_ldrex(&num);
}
```
```
> clang --target=armv7m-linux-gnueabi -S atomics.c -o -
atomics.c:3:5: error: address argument to load or store exclusive builtin must be a pointer to 1,2
      or 4 byte type ('volatile long long *' invalid)
    3 |     __builtin_arm_strex(42, &num);
      |     ^
atomics.c:4:12: error: address argument to load or store exclusive builtin must be a pointer to 1,2
      or 4 byte type ('const volatile long long *' invalid)
    4 |     return __builtin_arm_ldrex(&num);
      |            ^
2 errors generated.
```

However, a similar program would compile without errors:
```c
> type atomics.c
long long func(void) {
    long long num = 0;
    __builtin_arm_strexd(42, &num);
    return __builtin_arm_ldrexd(&num);
}
```
```
> clang --target=armv7m-linux-gnueabi -S atomics.c -o -
...
        strexd  r1, r2, r3, [r0]
        ldrexd  r0, r1, [r0]
...
```

With this change, we now have appropriate compile-time errors:
```
> clang --target=armv7m-linux-gnueabi -S atomics.c -o -
atomics.c:3:5: error: load and store exclusive builtins are not available on this architecture
    3 |     __builtin_arm_strexd(42, &num);
      |     ^                        ~~~~
atomics.c:4:12: error: load and store exclusive builtins are not available on this architecture
    4 |     return __builtin_arm_ldrexd(&num);
      |            ^                    ~~~~
2 errors generated.
```

0 files changed, 0 insertions, 0 deletions