Removed Android-specific code from stubs/hash.h

[acozzette]

This #ifdef in hash.h causes us to give up on finding a hash function on
Android, when there do seem to be hash functions available in practice.
I also had to tweak a macro in map.h that was disabling on Android an
allocator construct() method that we need.

[bazel-io]

Can one of the admins verify this patch?

[jbrianceau]

+1

This should solve errors I got with an android trybot on Chromium :

[UNKNOWN] PrecacheFetcherTest.PrecacheResourceSelection:
[ RUN      ] PrecacheFetcherTest.PrecacheResourceSelection
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:188] Should never be called.[ CRASHED      ]
[UNKNOWN] PrecacheFetcherTest.PrecacheResourceSelectionMissingBitset:
[ RUN      ] PrecacheFetcherTest.PrecacheResourceSelectionMissingBitset
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:188] Should never be called.[ CRASHED      ]
[UNKNOWN] TranslateRankerTest.CalculateScore:
[ RUN      ] TranslateRankerTest.CalculateScore
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:202] Should never be called.[ CRASHED      ]
[UNKNOWN] TranslateRankerTest.LoggingDisabled:
[ RUN      ] TranslateRankerTest.LoggingDisabled
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:202] Should never be called.[ CRASHED      ]
[UNKNOWN] TranslateRankerTest.RecordAndFlushEvents:
[ RUN      ] TranslateRankerTest.RecordAndFlushEvents
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:202] Should never be called.[ CRASHED      ]
[UNKNOWN] TranslateRankerTest.ShouldOfferTranslation:
[ RUN      ] TranslateRankerTest.ShouldOfferTranslation
[libprotobuf FATAL ../../third_party/protobuf/src/google/protobuf/stubs/hash.h:202] Should never be called.[ CRASHED      ]

[acozzette]

@jbrianceau Ah yes, I do think this should fix your test failures. The original symptom I saw was that exact crash. Let me know if you still see any issues after you test with this fix.