Use constexpr if to suppress more aggressive conversion warning The latest version of Clang started warning about the implicit conversion in the 'else' branch even for types where that branch is not taken. Use 'constexpr if' to passify the compiler. Bug: chromium:1487142 Change-Id: I52ae111abaeac46b586bf9f5c150c9a58e419704 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4891702 Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>