bpf: fix cross build failure on Debian

For compiling bpf code, the system include directory needs to be
constructed. On Debian-like systems, this requires passing a multiarch
directory. Since clang's -dump-machine prints something other that the
multiarch triplet, gcc was interrogated earlier, but that also yields a
wrong result for cross compilation and was thus skipped resulting in
clang not finding asm/types.h.

Rather than, -dump-machine we should ask for -print-multiarch (which
rarely differs). Whenever gcc is in use, this is right (even for cross
building). Since clang does not support -print-multiarch and its
-dump-machine never matches Debian's multiarch, we resort to asking gcc
when building natively. For cross builds using clang, we are out of
luck.

(cherry picked from commit 608009dc6218f7c41420f665586f2449b64a08f7)
(cherry picked from commit 1bd02a6e04270e6f01909cdc8b4e968f95ce5d4b)

meson.build

@@ -1754,15 +1754,22 @@ if conf.get('BPF_FRAMEWORK') == 1
 
         bpf_o_unstripped_cmd += ['-I.']
 
-        if not meson.is_cross_build()
-                target_triplet_cmd = run_command('gcc', '-dumpmachine', check: false)
-                if target_triplet_cmd.returncode() == 0
-                        target_triplet = target_triplet_cmd.stdout().strip()
-                        bpf_o_unstripped_cmd += [
-                                '-isystem',
-                                '/usr/include/@0@'.format(target_triplet)
-                        ]
+        if cc.get_id() == 'gcc' or meson.is_cross_build()
+                if cc.get_id() != 'gcc'
+                        warning('Cross compiler is not gcc. Guessing the target triplet for bpf likely fails.')
                 endif
+                target_triplet_cmd = run_command(cc.cmd_array(), '-print-multiarch', check: false)
+        else
+                # clang does not support -print-multiarch (D133170) and its -dump-machine
+                # does not match multiarch. Query gcc instead.
+                target_triplet_cmd = run_command('gcc', '-print-multiarch', check: false)
+        endif
+        if target_triplet_cmd.returncode() == 0
+                target_triplet = target_triplet_cmd.stdout().strip()
+                bpf_o_unstripped_cmd += [
+                        '-isystem',
+                        '/usr/include/@0@'.format(target_triplet)
+                ]
         endif
 
         bpf_o_unstripped_cmd += [