perf script python: Cope with declarations after statements found in Python.h

perf script python: Cope with declarations after statements found in Python.h

With -Werror the build was failing on fedora rawhide:

  [perfbuilder@27cfe44d67ed perf-6.5.0-rc2]$ gcc -v
  Using built-in specs.
  COLLECT_GCC=gcc
  COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/13/lto-wrapper
  OFFLOAD_TARGET_NAMES=nvptx-none
  OFFLOAD_TARGET_DEFAULT=1
  Target: x86_64-redhat-linux
  Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-libstdcxx-backtrace --with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-13.2.1-20230728/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none --without-cuda-driver --enable-offload-defaulted --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux --with-build-config=bootstrap-lto --enable-link-serialization=1
  Thread model: posix
  Supported LTO compression algorithms: zlib zstd
  gcc version 13.2.1 20230728 (Red Hat 13.2.1-1) (GCC)
  [perfbuilder@27cfe44d67ed perf-6.5.0-rc2]$

  In file included from /usr/include/python3.12/Python.h:44,
                   from scripts/python/Perf-Trace-Util/Context.c:14:
  /usr/include/python3.12/object.h: In function 'Py_SIZE':
  /usr/include/python3.12/object.h:217:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
    217 |     PyVarObject *var_ob = _PyVarObject_CAST(ob);
        |     ^~~~~~~~~~~
  In file included from /usr/include/python3.12/Python.h:53:
  /usr/include/python3.12/cpython/longintrepr.h: In function '_PyLong_CompactValue':
  /usr/include/python3.12/cpython/longintrepr.h:121:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
    121 |     Py_ssize_t sign = 1 - (op->long_value.lv_tag & _PyLong_SIGN_MASK);
        |     ^~~~~~~~~~
  <SNIP>
  In file included from /usr/include/python3.12/Python.h:44,
                   from util/scripting-engines/trace-event-python.c:22:
  /usr/include/python3.12/object.h: In function 'Py_SIZE':
  /usr/include/python3.12/object.h:217:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
    217 |     PyVarObject *var_ob = _PyVarObject_CAST(ob);
        |     ^~~~~~~~~~~
    CC      /tmp/build/perf/util/units.o
    CC      /tmp/build/perf/util/time-utils.o
  In file included from /usr/include/python3.12/Python.h:53:
  /usr/include/python3.12/cpython/longintrepr.h: In function '_PyLong_CompactValue':
  /usr/include/python3.12/cpython/longintrepr.h:121:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
    121 |     Py_ssize_t sign = 1 - (op->long_value.lv_tag & _PyLong_SIGN_MASK);
        |     ^~~~~~~~~~

So add -Wno-declaration-after-statement to the python scripting CFLAGS.

Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZMpdKeO8gU%2FcWDqH@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>