Wrap assert loops in #ifndef NDEBUG
Wrap assert loops in #ifndef NDEBUG

The body of the loops here only contained asserts.  This triggered an unused variable
warning on release builds and -Werror on the bots.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@240819 91177308-0d34-0410-b5e6-96231b3b80d8

dslab-epfl/asap,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm