perf tests bpf prologue: Fix bpf-script-test-prologue test compile issue with clang

While running 'perf test' for bpf, observed that "BPF prologue
generation" test case fails to compile with clang. Logs below from
powerpc:

  <stdin>:33:2: error: use of undeclared identifier 'fmode_t'
          fmode_t f_mode = (fmode_t)_f_mode;
          ^
  <stdin>:37:6: error: use of undeclared identifier 'f_mode'; did you mean '_f_mode'?
          if (f_mode & FMODE_WRITE)
              ^~~~~~
              _f_mode
  <stdin>:30:60: note: '_f_mode' declared here
  int bpf_func__null_lseek(void *ctx, int err, unsigned long _f_mode,
                                                             ^
  2 errors generated.

The test code tests/bpf-script-test-prologue.c uses fmode_t.  And the
error above is for "fmode_t" which is defined in include/linux/types.h
as part of kernel build directory: "/lib/modules/<kernel_version>/build"
that comes from kernel devel [ soft link to /usr/src/<kernel_version> ].

Clang picks this header file from "-working-directory" build option that
specifies this build folder.

But the commit 14e4b9f428 ("perf trace: Raw augmented syscalls fix
libbpf 1.0+ compatibility") changed the include directory to use:
"/usr/include".

Post this change, types.h from /usr/include/ is getting picked upwhich
doesn’t contain definition of "fmode_t" and hence fails to compile.

Compilation command before this commit:

  /usr/bin/clang -D__KERNEL__ -D__NR_CPUS__=72 -DLINUX_VERSION_CODE=0x50e00 -xc  -I/root/lib/perf/include/bpf -nostdinc -I./arch/powerpc/include -I./arch/powerpc/include/generated  -I./include -I./arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h  -Wno-unused-value -Wno-pointer-sign -working-directory /lib/modules/<ver>/build -c - -target bpf  -g -O2 -o -

Compilation command after this commit:

  /usr/bin/clang -D__KERNEL__ -D__NR_CPUS__=72 -DLINUX_VERSION_CODE=0x50e00 -xc  -I/usr/include/ -nostdinc -I./arch/powerpc/include -I./arch/powerpc/include/generated  -I./include -I./arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h  -Wno-unused-value -Wno-pointer-sign -working-directory /lib/modules/<ver>/build -c - -target bpf  -g -O2 -o -

The difference is addition of -I/usr/include/  in the first line which
is causing the error. Fix this by adding typedef for "fmode_t" in the
testcase to solve the compile issue.

Fixes: 14e4b9f428 ("perf trace: Raw augmented syscalls fix libbpf 1.0+ compatibility")
Signed-off-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Disha Goel <disgoel@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nageswara R Sastry <rnsastry@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/linux-perf-users/20230105120436.92051-1-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/bpf-script-test-prologue.c

@@ -20,6 +20,8 @@
 # undef if
 #endif
 
+typedef unsigned int __bitwise fmode_t;
+
 #define FMODE_READ		0x1
 #define FMODE_WRITE		0x2