c3f34d06be Make it clear which functions that are intended to be translation unit local (practicalswift)
Pull request description:
Make it clear which functions that are intended to be translation unit local. Do not share functions that are meant to be translation unit local with other translation units. Use internal linkage for those consistently.
Partial Backport of Core PR13163 (support/lockedpool.cpp)
Part of breaking up D3293