Previously using format_hex() would always print a 0x prior to the
hex characters. This allows this to be optional, so that one can
choose to print (e.g.) 255 as either 0xFF or just FF.
Differential Revision: http://reviews.llvm.org/D7151
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227108 91177308-0d34-0410-b5e6-96231b3b80d8