[DebugInfo][X86] Fix handling of DBG_VALUE's in post-RA scheduler.

This patch fixes a bug with the updating of DBG_VALUE's in
BreakAntiDependencies. Previously, it would only attempt to update the first
DBG_VALUE following the instruction whose register is being changed,
potentially leaving DBG_VALUE's referring to the wrong register. Now the code
will update all DBG_VALUE's that immediately follow the instruction.

This issue was detected as a result of an optimized codegen difference with
"-g" where an X86 byte/word fixup was not performed due to a DBG_VALUE
referencing the wrong register.

Differential Revision: https://reviews.llvm.org/D31755

llvm-svn: 301309