BSLS_IDENT_PRAGMA_ONCE for MSVC
BSLS_IDENT_PRAGMA_ONCE for MSVC

MSVC supports '__pragma(once)', so use that for 'BSLS_IDENT_PRAGMA_ONCE'.

Signed-Off-By: Daryl Haresign <5c7773707c7f9db14f9d3723865bd5ffb16b7680@bloomberg.net>

apaprocki/bde,osubboo/bde,minhlongdo/bde,frutiger/bde,idispatch/bde,dharesign/bde,idispatch/bde,jmptrader/bde,dbremner/bde,osubboo/bde,apaprocki/bde,dharesign/bde,bloomberg/bde-allocator-benchmarks,bloomberg/bde-allocator-benchmarks,che2/bde,bloomberg/bde,bloomberg/bde,bowlofstew/bde,gbleaney/Allocator-Benchmarks,minhlongdo/bde,jmptrader/bde,che2/bde,mversche/bde,apaprocki/bde,frutiger/bde,saxena84/bde,minhlongdo/bde,RMGiroux/bde-allocator-benchmarks,gbleaney/Allocator-Benchmarks,bowlofstew/bde,idispatch/bde,saxena84/bde,bloomberg/bde-allocator-benchmarks,che2/bde,che2/bde,bloomberg/bde-allocator-benchmarks,osubboo/bde,apaprocki/bde,frutiger/bde,bloomberg/bde,minhlongdo/bde,bowlofstew/bde,mversche/bde,dbremner/bde,gbleaney/Allocator-Benchmarks,jmptrader/bde,dbremner/bde,saxena84/bde,RMGiroux/bde-allocator-benchmarks,gbleaney/Allocator-Benchmarks,bloomberg/bde-allocator-benchmarks,idispatch/bde,frutiger/bde,RMGiroux/bde-allocator-benchmarks,mversche/bde,jmptrader/bde,osubboo/bde,dbremner/bde,bowlofstew/bde,saxena84/bde,RMGiroux/bde-allocator-benchmarks,dharesign/bde,dharesign/bde,mversche/bde,bloomberg/bde,apaprocki/bde,bloomberg/bde,RMGiroux/bde-allocator-benchmarks