Generally speaking, mips-* vs mips64-* should not be used to make decisions
about the content or format of the ELF. This should be based on the ABI
and CPU in use. For example, mips-linux-gnu-clang -mips64r2 -mabi=64
should produce an ELF64 as should mips64-linux-gnu-clang -mabi=64.
Conversely, mips64-linux-gnu-clang -mabi=n32 should produce an ELF32 as
should mips-linux-gnu-clang -mips64r2 -mabi=n32.
This patch fixes the e_flags but leaves the ELF32 vs ELF64 issue for now
since there is no apparent way to base this decision on the ABI and CPU.