[dsymutil] Apply relocations to DIE data before cloning.

Doing this gets function's low_pc and global variable's locations right
in the output debug info. It also could get right other attributes
that need to be relocated (in linker terms), but I don't know of any
other than the address attributes.

This doesn't fixup low_pc attributes in compile_unit, lexical_block
or inlined subroutine, nor does it get right high_pc attributes
for function. This will come in a subsequent commit.

llvm-svn: 231544