uapi: Fix undefined __always_inline on non-glibc systems

uapi: Fix undefined __always_inline on non-glibc systems

This macro is defined by glibc itself, which makes the issue go unnoticed on
those systems.  On non-glibc systems it causes build failures on several
utilities and libraries, like bpftool and objtool.

Fixes: 79fb0d2bf5b0 ("x86/insn: Support big endian cross-compiles")
Fixes: 00d4f8e81c2e ("tools/virtio: more stubs")
Fixes: cface3daf21f ("selftests/net: ipv6 flowlabel")
Fixes: 8f6ecdaf3d4a ("selftests/bpf: test bpf flow dissection")
Fixes: 91111edc337d ("bpf: Remove extra lock_sock for TCP_ZEROCOPY_RECEIVE")
Fixes: b8a7cb8c2d74 ("tools include uapi: Grab a copy of linux/in.h")
Fixes: a0fbb20d0b00 ("bpf: btf: add btf print functionality")
Fixes: 223dff668a92 ("tools, include: Grab a copy of linux/erspan.h")
Fixes: f946538ba200 ("tools: Add copy of perf_event.h to tools/include/linux/")
Signed-off-by: Ismael Luceno <ismael@iodev.co.uk>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211115134647.1921-1-ismael@iodev.co.uk
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>