Fix a few symbols that are not actually ABS.

The symbols _end, end, _etext, etext, _edata, edata and __ehdr_start
refer to positions in the file and are therefore not absolute. Making
them absolute was on unfortunate cargo cult of what bfd was doing.

Changing the symbols allows for pc relocations to them to be resolved,
which should fix the wine build.

llvm-svn: 293385