Remove duplicate _LIBCPP_INLINE_VISIBILITY attributes.
Remove duplicate _LIBCPP_INLINE_VISIBILITY attributes.

This attribute should appear only on the first declaration. This
patch cleans up <string> by removing the attribute on redeclarations.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@347608 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx