[ARM][BZ #17711] Fix extern protected data handling

Fixes elf/tst-protected1a and elf/tst-protected1b tests.

Depends on a gcc patch that makes protected visibility data non-local:
https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01871.html
and on a binutils patch so R_*_GLOB_DAT relocs are used for it:
https://sourceware.org/ml/binutils/2015-07/msg00247.html