[CodeView] Mark our lines as statements, not expressions

[CodeView] Mark our lines as statements, not expressions

The line tables for CodeView make a distinction between expressions and
statements.  As it turns out, MSVC always emits them as statements and
we always emit them as expressions.  Let's switch to statements to match
the CodeView that they emit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257553 91177308-0d34-0410-b5e6-96231b3b80d8