[AIX] Bump DWARF versions to 3 because XCOFF64 requires DWARF64

DWARF64 was implemented at version 3, so if a DWARF version less than 3 is specified, DWARF64 does not get selected. Since XCOFF64 requires DWARF64, the modified tests fail on 64-bit AIX. This patch bumps these tests to dwarf version 3 to maintain test coverage on 64-bit AIX.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D114110