[lld] Correct forming of ARM/Thumb atoms

Symbols addressing Thumb code have zero bit set in st_value to distinguish them from ARM instructions.
This caused wrong atoms' forming because of offset of one byte brought in by that corrected st_value.

Fixed reading of st_value & st_value-related things in ARMELFFile while forming atoms.
Symbol table generation is also fixed for Thumb atoms.

Differential Revision: http://reviews.llvm.org/D7161

llvm-svn: 227174