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

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

With test-case gdb.base/infoline-reloc-main-from-zero.exp and target board
unix/-fPIE/-pie I run into:
...
gdb compile failed, ld: infoline-reloc-main-from-zero: error: \
  PHDR segment not covered by LOAD segment
collect2: error: ld returned 1 exit status
...

When running with native, I find that the executable is static:
...
$ file infoline-reloc-main-from-zero
infoline-reloc-main-from-zero: ELF 64-bit LSB executable, x86-64, \
  version 1 (SYSV), statically linked, BuildID[sha1]=$hex, with debug_info, \
  not stripped
...
despite not having been compiled with -static.

Fix the compilation by adding -static to the compilation flags.

Tested on x86_64-linux.