[compiler-rt] Add CMake flag for AArch64 Linux with 39-bit VA. (#167028)

Sanitizers currently assume AArch64 Linux has 48-bit VA. Followup
patches will add checks for this flag to asan and hwasan.

GitOrigin-RevId: 58c8f5768102751ce932b597563aaa4a3b7fa430
1 file changed