__ILP32__/__LP64__ instead of by architecture.
The list was incomplete (previous commits purged invalid architectures,
like __alpha__, but failed to add new ones). It's best to base the symbol
presence on whether or not the architecture is ILP32 / LP64 capable, per
the compiler.
This fixes the ILP32/LP64 program environments on some architectures like
arm64, and by proxy fixes the tests on those architectures.
MFC after: 1 month
Reviewed by: no one (timed out on feedback from imp)
Differential Revision: D10787
7250a09527