more efficient memory barriers in bsl atomics on x86/64
Add benchmark test
Update performance tests
Remove mfence from getInt operations
Changed integral implementations to identity.

Test driver needs checking.
Changed test cases to recognize identity hash.
Fixed bdeflag concerns in the header.
Changed hashing algorithm for 32-bit.
Clarified the reasoning in comments and CT-asserts
Added a test for 32-bit mangling.
Merge branch 'testing_for_mangling' into review/hash_optimize_by_identity-drqs-46166503
bump version to 2.20, and update bdlscm to use s_ prefixes
fix unintended cpp11 string literal operator issue
Clean up 64-bit warnings in hash table

This patch clears up just under 1300 warnings when building the hash
table test driver on a 64-bit platform.  Most of the warnings arise
from using a test allocator which deliberately supports only a 32-bit
address space, i.e., has a narrower 'size_type' than 'std::size_t'.

We do not yet have a test allocator to verify behavior when 'size_type'
is *wider* than 'std::size_t', but that appears less useful for this
specific data structure, as the standard hash-function requirements
include that the function returns a 'std::size_t', so even if we can
allocate more memory, we literally cannot address more buckets due to
the granularity of the hash function.
[APPROVAL] INTERNAL warnings-merge-drqs-41944020 to master

Base commit: 74e0564188ec61977963ec8af7f6de83e687c128
add bslmf_assert
[APPROVAL] pending/master/cleanup_64bit_warnings_in_hashtable_drqs48504031 to master
adjust white space
Fix build errors and warnings for gcc
[APPROVAL] pending/master/hash_optimize_by_identity-drqs-46166503 to master