SFINAE out duration converting constructor if the constructor would otherwise cause a ratio compile-time overflow.  This fixes LWG 2094.

llvm-svn: 189722
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 69bc206547c3b9f413673ef0ebc6e425c6dbd11a
3 files changed