Similar to D74882. This reverts much code from commit bd8cfe65f5fee4ad573adc2172359c9552e8cdc0 (D68323) and fixes some problems before D68323. Sorry for the churn but D68323 was a mistake. Namespace qualifiers avoid bugs where the definition does not match the declaration from the header. See https://llvm.org/docs/CodingStandards.html#use-namespace-qualifiers-to-implement-previously-declared-functions (D74515) Differential Revision: https://reviews.llvm.org/D79982