more efficient memory barriers in bsl atomics on x86/64
Add benchmark test
Update performance tests
s/d_allocator/d_allocator_p/ where needed in bsl
Remove mfence from getInt operations
C++11 atomics using gcc and clang intrinsics
Uncompilable expression fixed.

hash<char16_t>::operator()(char16_t) const
and
hash<char32_t>::operator()(char16_t) const

were improperly declared as:

hash<char>::operator()(char16_t) const
and
hash<char>::operator()(char16_t) const

The test driver and platform specific components need inspection to find out
why this was not discovered.
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
Updated the waf build tool to support compiling c packages, std-alone packages, and package groups in the enterprise sub-directory.
fix unintended cpp11 string literal operator issue
Added support for overriding the detected uplid with the BDE_WAF_UPLID environment variable.
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.
Fixed the running of tests for repos that do not contain the BDE waf customization scripts.