Support allocators with explicit conversion constructors. Fixes bug #29000

llvm-svn: 278904
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 2a10c960fa33b7048b48107823f5879cf301dece
41 files changed