[ARM] Update R_ARM_TARGET1 command line option names (remove prefix 'arm-')

Command line options --arm-target1-rel and --arm-target1-abs have been renamed to be compatible with GNU linkers.
Two tests have been updated:
  test/elf/options/target-specific-args.test
  test/elf/ARM/rel-arm-target1.test

Differential Revision: http://reviews.llvm.org/D9037

llvm-svn: 235499