bpf, mips: Fix build errors about __NR_bpf undeclared

Add the __NR_bpf definitions to fix the following build errors for mips.

 $ cd tools/bpf/bpftool
 $ make
 [...]
 bpf.c:54:4: error: #error __NR_bpf not defined. libbpf does not support your arch.
  #  error __NR_bpf not defined. libbpf does not support your arch.
     ^~~~~
 bpf.c: In function ‘sys_bpf’:
 bpf.c:66:17: error: ‘__NR_bpf’ undeclared (first use in this function); did you mean ‘__NR_brk’?
   return syscall(__NR_bpf, cmd, attr, size);
                  ^~~~~~~~
                  __NR_brk
 [...]
 In file included from gen_loader.c:15:0:
 skel_internal.h: In function ‘skel_sys_bpf’:
 skel_internal.h:53:17: error: ‘__NR_bpf’ undeclared (first use in this function); did you mean ‘__NR_brk’?
   return syscall(__NR_bpf, cmd, attr, size);
                  ^~~~~~~~
                  __NR_brk

We can see the following generated definitions:

 $ grep -r "#define __NR_bpf" arch/mips
 arch/mips/include/generated/uapi/asm/unistd_o32.h:#define __NR_bpf (__NR_Linux + 355)
 arch/mips/include/generated/uapi/asm/unistd_n64.h:#define __NR_bpf (__NR_Linux + 315)
 arch/mips/include/generated/uapi/asm/unistd_n32.h:#define __NR_bpf (__NR_Linux + 319)

The __NR_Linux is defined in arch/mips/include/uapi/asm/unistd.h:

 $ grep -r "#define __NR_Linux" arch/mips
 arch/mips/include/uapi/asm/unistd.h:#define __NR_Linux	4000
 arch/mips/include/uapi/asm/unistd.h:#define __NR_Linux	5000
 arch/mips/include/uapi/asm/unistd.h:#define __NR_Linux	6000

That is to say, __NR_bpf is
4000 + 355 = 4355 for mips o32,
6000 + 319 = 6319 for mips n32,
5000 + 315 = 5315 for mips n64.

So use the GCC pre-defined macro _ABIO32, _ABIN32 and _ABI64 [1] to define
the corresponding __NR_bpf.

This patch is similar with commit bad1926 ("bpf, s390: fix build for
libbpf and selftest suite").

[1] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/mips/mips.h#l549

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>

tools/build/feature/test-bpf.c

@@ -14,6 +14,12 @@
 #  define __NR_bpf 349
 # elif defined(__s390__)
 #  define __NR_bpf 351
+# elif defined(__mips__) && defined(_ABIO32)
+#  define __NR_bpf 4355
+# elif defined(__mips__) && defined(_ABIN32)
+#  define __NR_bpf 6319
+# elif defined(__mips__) && defined(_ABI64)
+#  define __NR_bpf 5315
 # else
 #  error __NR_bpf not defined. libbpf does not support your arch.
 # endif

tools/lib/bpf/bpf.c

@@ -50,6 +50,12 @@
 #  define __NR_bpf 351
 # elif defined(__arc__)
 #  define __NR_bpf 280
+# elif defined(__mips__) && defined(_ABIO32)
+#  define __NR_bpf 4355
+# elif defined(__mips__) && defined(_ABIN32)
+#  define __NR_bpf 6319
+# elif defined(__mips__) && defined(_ABI64)
+#  define __NR_bpf 5315
 # else
 #  error __NR_bpf not defined. libbpf does not support your arch.
 # endif

tools/lib/bpf/skel_internal.h

@@ -7,6 +7,16 @@
 #include <sys/syscall.h>
 #include <sys/mman.h>
 
+#ifndef __NR_bpf
+# if defined(__mips__) && defined(_ABIO32)
+#  define __NR_bpf 4355
+# elif defined(__mips__) && defined(_ABIN32)
+#  define __NR_bpf 6319
+# elif defined(__mips__) && defined(_ABI64)
+#  define __NR_bpf 5315
+# endif
+#endif
+
 /* This file is a base header for auto-generated *.lskel.h files.
  * Its contents will change and may become part of auto-generation in the future.
  *