This will fix remaining failures on gcc-9 buildbot: http://lab.llvm.org:8011/#/builders/101. gcc-8 and gcc-9 do not support constexpr destructors nor constexpr allocation. Fix gcc warnings: -Wconversion, -Wpragmas.  | 
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| .. | ||
| allocator.globals | ||
| allocator.members | ||
| allocator.ctor.pass.cpp | ||
| allocator.dtor.pass.cpp | ||
| allocator_pointers.pass.cpp | ||
| allocator_types.deprecated_in_cxx17.verify.cpp | ||
| allocator_types.pass.cpp | ||
| allocator_types.removed_in_cxx20.verify.cpp | ||
| allocator_void.deprecated_in_cxx17.verify.cpp | ||