[gdb/testsuite] Fix gdb.base/infoline-reloc-main-from-zero.exp with recent ld

On openSUSE Tumbleweed (with ld 2.39) and test-case
gdb.base/infoline-reloc-main-from-zero.exp, I get:
...
gdb compile failed, ld: warning: infoline-reloc-main-from-zero has a LOAD \
  segment with RWX permissions
UNTESTED: gdb.base/infoline-reloc-main-from-zero.exp: \
  infoline-reloc-main-from-zero.exp
...

Fix this by compiling with -Wl,--no-warn-rwx-segments.

Tested on x86_64-linux.