Build error with GCC git head (Nov 2021)

[paulfloyd]

Running buildcmd.sh gives me

[ 14%] Building C object CMakeFiles/bpf.dir/lib/bpf/src/libbpf_errno.c.o
.../dwarves/lib/bpf/src/gen_loader.c: In function 'get_ksym_desc':
.../dwarves/lib/bpf/src/gen_loader.c:585:2: error: 'for' loop initial declarations are only allowed in C99 mode
  for (int i = 0; i < gen->nr_ksyms; i++) {
  ^
.../dwarves/lib/bpf/src/gen_loader.c:585:2: note: use option -std=c99 or -std=gnu99 to compile your code
make[2]: *** [CMakeFiles/bpf.dir/lib/bpf/src/gen_loader.c.o] Error 1
make[2]: *** Waiting for unfinished jobs....
.../dwarves/lib/bpf/src/btf_dump.c: In function 'btf_dump_dump_type_data.isra.24':
.../dwarves/lib/bpf/src/btf_dump.c:2274:5: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (err < 0)
     ^