This reverts commit 9fe769a961dc8e3ce7d967ea0e07a4f0e5fac6e9, and re-lands commit c2e272f8cf76ec97f675e0dfdada75445bbee5c5.
Summary: Add support for ?, DUP, and string initializers, as well as MASM syntax for named data locations.
This version avoids the use of a C++17-only feature, if-statements with initializer.
Reviewers: rnk, thakis
Reviewed By: thakis
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73226