Omit .gnu_debuglink sections in object files

I'm not sure if these sections are used, but by adding them to
libgcc_stripped.a, we can end up with multiple .gnu_debuglink sections in
an executable, where the first two unhelpfully point at "libgcc.a". e.g.:

$ readelf -SW -x.gnu_debuglink out/target/product/walleye/system/bin/bootstrap/linker64
...

Section Headers:
  ...
  [18] .gnu_debuglink    PROGBITS        0000000000000000 10f19c 000020 00      0   0  1
  ...
  [22] .gnu_debuglink    PROGBITS        0000000000000000 18a2c8 000010 00      0   0  4
  ...

Hex dump of section '.gnu_debuglink':
  0x00000000 6c696267 63632e61 00000000 3d5f65d8 libgcc.a....=_e.
  0x00000010 6c696267 63632e61 00000000 3d5f65d8 libgcc.a....=_e.

Hex dump of section '.gnu_debuglink':
  0x00000000 6c696e6b 65723634 00000000 f85db7ea linker64.....]..

Bug: none
Test: m libgcc_stripped linker
Test: no .gnu_debuglink section in libgcc_stripped.a
Test: only one .gnu_debuglink section in system/bin/bootstrap/linker64
Change-Id: I0c47a9acd6d52f5cbc5bfa8b67d072ebb075a242