[codeview] omit debug locations for nested exprs unless column info enabled

Summary:
Microsoft Visual Studio expects debug locations to correspond to
statements. We used to emit locations for expressions nested inside statements.
This would confuse the debugger, causing it to stop multiple times on the
same line and breaking the "step into specific" feature. This change inhibits
the emission of debug locations for nested expressions when emitting CodeView
debug information, unless column information is enabled.

Fixes PR34312.

Reviewers: rnk, zturner

Reviewed By: rnk

Subscribers: majnemer, echristo, aprantl, cfe-commits

Differential Revision: https://reviews.llvm.org/D37529

llvm-svn: 312965