libbpf: Disable SEC pragma macro on GCC

It seems the gcc preprocessor breaks with pragmas when surrounding
__attribute__.

Disable these pragmas on GCC due to upstream bugs see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55578
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90400



Fixes errors like:
error: expected identifier or '(' before '#pragma'
  106 | SEC("cgroup/bind6")
      | ^~~

error: expected '=', ',', ';', 'asm' or '__attribute__' before '#pragma'
  114 | char _license[] SEC("license") = "GPL";
      | ^~~

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220706111839.1247911-1-james.hilliard1@gmail.com