When instantiating statements that involve conditions (if, while, do,

When instantiating statements that involve conditions (if, while, do,
for, and switch), be careful to construct the full expressions as soon
as we perform template instantation, so we don't either forget to call
temporary destructors or destroy temporaries at the wrong time. This
is the template-instantiation analogue to r103187, during which I
hadn't realized that the issue would affect the handling of these
constructs differently inside and outside of templates.

Fixes a regression in Boost.Function.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@103357 91177308-0d34-0410-b5e6-96231b3b80d8