[CodeGen] Use IRBuilder to create llvm.lifetime intrinsics.

Summary:
In addition to easier syntax, IRBuilder makes sure to set correct
debug locations for newly added instructions (bitcast and
llvm.lifetime itself). This restores the original behavior, which
was modified by r234581 (reapplied as r235553).

Extend one of the tests to check for debug locations.

Test Plan: regression test suite

Reviewers: aadg, dblaikie

Subscribers: cfe-commits, majnemer

Differential Revision: http://reviews.llvm.org/D10418

llvm-svn: 239643