perf clang: Fixes for more recent LLVM/clang

The parameters to two functions and the location of a variable have
changed in more recent LLVM/clang releases.

Remove the unneecessary -fmessage-length and -ferror-limit flags, the
former causes failures like:

  58: builtin clang support                                           :
  58.1: builtin clang compile C source to IR                          :
  --- start ---
  test child forked, pid 279307
  error: unknown argument: '-fmessage-length'
  1 error generated.
  test child finished with -1

Tested with LLVM 6, 8, 9, 10 and 11.

Reviewed-by: Fangrui Song <maskray@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sedat Dilek <sedat.dilek@gmail.com>,
Cc: llvm@lists.linux.dev
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>