perf: silence GTK2 probing errors

perf: silence GTK2 probing errors

If GTK2 development packages are not installed, make is rather noisy:

  $ make -C tools/perf O=/tmp/pbuild
  Package gtk+-2.0 was not found in the pkg-config search path.
  Perhaps you should add the directory containing `gtk+-2.0.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'gtk+-2.0' found
  make: Entering directory `/opt/sw/ahern/perf.git/tools/perf'
  Makefile:593: GTK2 not found, disables GTK2 support. Please install gtk2-devel or libgtk2.0-dev
  PERF_VERSION = 3.6.rc1.205.gdb146f.dirty
  make: Leaving directory `/opt/sw/ahern/perf.git/tools/perf'
  Package gtk+-2.0 was not found in the pkg-config search path.
  Perhaps you should add the directory containing `gtk+-2.0.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'gtk+-2.0' found
  make: Entering directory `/opt/sw/ahern/perf.git/tools/perf'
  Makefile:593: GTK2 not found, disables GTK2 support. Please install gtk2-devel or libgtk2.0-dev
  ...

Silence the pkg-config errors. Aftewards:

  $ make -C tools/perf O=/tmp/pbuild
  make: Entering directory `/opt/sw/ahern/perf.git/tools/perf'
  Makefile:593: GTK2 not found, disables GTK2 support. Please install gtk2-devel or libgtk2.0-dev
  PERF_VERSION = 3.6.rc1.206.gd43ff9.dirty
  make: Leaving directory `/opt/sw/ahern/perf.git/tools/perf'
  make: Entering directory `/opt/sw/ahern/perf.git/tools/perf'
  Makefile:593: GTK2 not found, disables GTK2 support. Please install gtk2-devel or libgtk2.0-dev
  ...

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/1345391202-71865-1-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>