COMP: Resolve clang linkage issue
COMP: Resolve clang linkage issue

A recent commit
ChangeId: I37a03ab4004fe1e4e0160ae13e6bac4fc5eee781
to fix duplicate link symbols on VS10 and VS11 introduced unresolved
references with sonme versions of the mac clang++ compiler. This patch
removes the ITK_CONSTEXPR's for windows builds only.

Change-Id: Id22085483f6e8f00d8444d4416c259f506d25d06

stnava/ITK,richardbeare/ITK,LucasGandel/ITK,blowekamp/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,blowekamp/ITK,BRAINSia/ITK,PlutoniumHeart/ITK,vfonov/ITK,Kitware/ITK,thewtex/ITK,zachary-williamson/ITK,vfonov/ITK,PlutoniumHeart/ITK,thewtex/ITK,hjmjohnson/ITK,LucasGandel/ITK,stnava/ITK,PlutoniumHeart/ITK,zachary-williamson/ITK,malaterre/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,blowekamp/ITK,malaterre/ITK,PlutoniumHeart/ITK,zachary-williamson/ITK,fbudin69500/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,Kitware/ITK,zachary-williamson/ITK,malaterre/ITK,Kitware/ITK,LucasGandel/ITK,zachary-williamson/ITK,thewtex/ITK,blowekamp/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,vfonov/ITK,richardbeare/ITK,PlutoniumHeart/ITK,spinicist/ITK,spinicist/ITK,BRAINSia/ITK,richardbeare/ITK,vfonov/ITK,hjmjohnson/ITK,stnava/ITK,zachary-williamson/ITK,LucasGandel/ITK,spinicist/ITK,fbudin69500/ITK,fbudin69500/ITK,spinicist/ITK,PlutoniumHeart/ITK,fbudin69500/ITK,stnava/ITK,richardbeare/ITK,malaterre/ITK,vfonov/ITK,malaterre/ITK,PlutoniumHeart/ITK,malaterre/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,LucasGandel/ITK,richardbeare/ITK,fbudin69500/ITK,spinicist/ITK,BRAINSia/ITK,spinicist/ITK,Kitware/ITK,richardbeare/ITK,stnava/ITK,stnava/ITK,blowekamp/ITK,thewtex/ITK,zachary-williamson/ITK,malaterre/ITK,spinicist/ITK,hjmjohnson/ITK,richardbeare/ITK,LucasGandel/ITK,hjmjohnson/ITK,fbudin69500/ITK,PlutoniumHeart/ITK,spinicist/ITK,BRAINSia/ITK,vfonov/ITK,stnava/ITK,spinicist/ITK,zachary-williamson/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,thewtex/ITK,vfonov/ITK,malaterre/ITK,stnava/ITK,hjmjohnson/ITK,stnava/ITK,fbudin69500/ITK,vfonov/ITK,thewtex/ITK,blowekamp/ITK,fbudin69500/ITK,zachary-williamson/ITK,BRAINSia/ITK,blowekamp/ITK,Kitware/ITK,blowekamp/ITK