By adding a feature test for bpf_map_create() and providing a fallback if
it isn't present in older versions of libbpf.

This also fixes the build with torvalds/master at this point:

  $ git log --oneline -5 torvalds/master
  babf0bb9 (torvalds/master) Merge tag 'xfs-5.19-for-linus' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux
  e375780b Merge tag 'fsnotify_for_v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs
  8b728edc Merge tag 'fs_for_v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs
  3f306ea2 Merge tag 'dma-mapping-5.19-2022-05-25' of git://git.infradead.org/users/hch/dma-mapping
  fbe86dac Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
  $

Coping with:

  $ git log --oneline -2 d16495a9
  d16495a9 libbpf: remove bpf_create_map*() APIs
  e2371b16 libbpf: start 1.0 development cycle
  $

As the __weak function fails to build as it calls the now removed
bpf_create_map() API.

Testing:

  $ rpm -q libbpf-devel
  libbpf-devel-0.4.0-2.fc35.x86_64
  $
  $ make -C tools/perf BUILD_BPF_SKEL=1 LIBBPF_DYNAMIC=1 O=/tmp/build/perf install-bin
  $ cat /tmp/build/perf/feature/test-libbpf-bpf_map_create.make.output
  test-libbpf-bpf_map_create.c: In function ‘main’:
  test-libbpf-bpf_map_create.c:6:16: error: implicit declaration of function ‘bpf_map_create’; did you mean ‘bpf_map_freeze’? [-Werror=implicit-function-declaration]
      6 |         return bpf_map_create(0 /* map_type */, NULL /* map_name */, 0, /* key_size */,
        |                ^~~~~~~~~~~~~~
        |                bpf_map_freeze
  test-libbpf-bpf_map_create.c:6:87: error: expected expression before ‘,’ token
      6 |         return bpf_map_create(0 /* map_type */, NULL /* map_name */, 0, /* key_size */,
        |                                                                                       ^
  cc1: all warnings being treated as errors
  $
  $ objdump -dS /tmp/build/perf/perf | grep '<bpf_map_create>:' -A20
  000000000058b290 <bpf_map_create>:
  {
    58b290:	55                   	push   %rbp
    58b291:	48 89 e5             	mov    %rsp,%rbp
    58b294:	48 83 ec 10          	sub    $0x10,%rsp
    58b298:	64 48 8b 04 25 28 00 	mov    %fs:0x28,%rax
    58b29f:	00 00
    58b2a1:	48 89 45 f8          	mov    %rax,-0x8(%rbp)
    58b2a5:	31 c0                	xor    %eax,%eax
  	return bpf_create_map(map_type, key_size, value_size, max_entries, 0);
    58b2a7:	48 8b 45 f8          	mov    -0x8(%rbp),%rax
    58b2ab:	64 48 2b 04 25 28 00 	sub    %fs:0x28,%rax
    58b2b2:	00 00
    58b2b4:	75 10                	jne    58b2c6 <bpf_map_create+0x36>
  }
    58b2b6:	c9                   	leave
    58b2b7:	89 d6                	mov    %edx,%esi
    58b2b9:	89 ca                	mov    %ecx,%edx
    58b2bb:	44 89 c1             	mov    %r8d,%ecx
  	return bpf_create_map(map_type, key_size, value_size, max_entries, 0);
    58b2be:	45 31 c0             	xor    %r8d,%r8d
  $

Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/linux-perf-users/Yo+XvQNKL4K5khl2@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>