libbpf: Silence newly-added and unused sections

With latest llvm22, when building bpf selftest, I got the following info
emitted by libbpf:
  ...
  libbpf: elf: skipping unrecognized data section(14) .comment
  libbpf: elf: skipping section(15) .note.GNU-stack (size 0)
  ...

The reason is due to llvm patch [1]. Previously, bpf class BPFMCAsmInfo
inherits class MCAsmInfo. With [1], BPFMCAsmInfo inherits class
MCAsmInfoELF. Such a change added two more sections in the bpf binary, e.g.
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  ...
  [23] .comment          PROGBITS        0000000000000000 0035ac 00006d 01  MS  0   0  1
  [24] .note.GNU-stack   PROGBITS        0000000000000000 003619 000000 00      0   0  1
  ...

Adding the above two sections in elf section ignore list can avoid the
above info dump during selftest build.

  [1] llvm/llvm-project@d9489fd

Signed-off-by: Yonghong Song <[email protected]>

Author: Yonghong Song

tools/lib/bpf/libbpf.c

@@ -3788,6 +3788,14 @@ static bool ignore_elf_section(Elf64_Shdr *hdr, const char *name)
 	if (is_sec_name_dwarf(name))
 		return true;
 
+	/* .comment section */
+	if (strcmp(name, ".comment") == 0)
+		return true;
+
+	/* .note.GNU-stack section */
+	if (strcmp(name, ".note.GNU-stack") == 0)
+		return true;
+
 	if (str_has_pfx(name, ".rel")) {
 		name += sizeof(".rel") - 1;
 		/* DWARF section relocations */