Subzero: Fix floating-point constant pooling.
This fixes a regression likely introduced in
d2cb4361c732dcddc98659415f37be45982e20c3 .
The problem is that by using the default std::unordered_map comparison predicate std::equal_to, we get incorrect behavior when the key is float or double:
1. 0.0 and -0.0 appear equal, so they share a constant pool entry even though the bit patterns are different. This is a correctness bug.
2. Each instance of NaN gets a separate constant pool entry, because NaN != NaN by C equality rules. This is a performance bug. (This problem doesn't show up with the native bitcode reader, because constants are already unique-ified in the PNaCl bitcode file.)
The solution is to use memcmp for floating-point key types.
Also, the abi-atomics.ll test is disabled for the MINIMAL build, to fix an oversight from a previous CL.
BUG= none
R=jfb@chromium.org
Review URL: https://codereview.chromium.org/
1019233002