Make it clear where is a placeholder for later binary patching.

This is an aesthetic change to represent a placeholder for later
binary patching as "0, 0, 0, 0" instead of "0x00, 0x00, 0x00, 0x00".
The former is how we represent it in COFF, and I found it easier to
read than the latter.

llvm-svn: 321471