Fix PR30642 -  libc++ leaks always-visible symbols into programs
Fix PR30642 -  libc++ leaks always-visible symbols into programs

This was caused by r281673, specifically changing `_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS`
from `__attribute__((__type_visibility__("default")))` to
`__attribute__((__visibility("default")))`.

I made that change because I thought the external instantiations needed
their members to have default visibility. However since libc++ never builds
with -fvisibility=hidden this appears not to be needed. Instead this change
caused previously hidden inline methods to become un-hidden, which is a regression.

This patch reverts the problematic change and fixes PR30642.


git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@283620 91177308-0d34-0410-b5e6-96231b3b80d8

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