[CodeGenPrepare] Scan past debug intrinsics to find select candidates (NFC)

In optimizeSelectInst, when scanning for candidate selects to rewrite
into branches, scan past debug intrinsics. This makes the debug-enabled
and non-debug paths through optimizeSelectInst more congruent.

NFC because every select is eventually visited either way.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340368 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed