Move external instantiation for __vector_base_common to vector.cpp

Previously the explicit instantiation for this was in locale.cpp,
but that didn't make much sense. This patch creates a new vector.cpp
source file to contain the explicit instantiation.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@305442 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed