[clang] Do not instrument relative vtables under hwasan
Full context in
https://bugs.fuchsia.dev/p/fuchsia/issues/detail?id=107017.
Instrumenting hwasan with globals results in a linker error under the
relative vtables abi:
```
ld.lld: error:
libunwind.cpp:(.rodata..L_ZTVN9libunwind12UnwindCursorINS_17LocalAddressSpaceENS_15Registers_arm64EEE.hwasan+0x8):
relocation R_AARCH64_PLT32 out of range:
6845471433603167792 is not in
[-
2147483648,
2147483647]; references
libunwind::AbstractUnwindCursor::~AbstractUnwindCursor()
>>> defined in
libunwind/src/CMakeFiles/unwind_shared.dir/libunwind.cpp.obj
```
This is because the tag is included in the vtable address when
calculating the offset between the vtable and virtual function. A
temporary solution until we can resolve this is to just disable hwasan
instrumentation on relative vtables specifically, which can be done in
the frontend.
Differential Revision: https://reviews.llvm.org/D132425