portaudio: inherit pkgconfig

* without pkgconfig it's failing to expand PKG_CHECK_MODULES macro:
  | portaudio-v19/v19+svnr1387-r0/trunk/configure:
    line 11721: syntax error near unexpected token `JACK,'
  | portaudio-v19/v19+svnr1387-r0/trunk/configure:
    line 11721: `PKG_CHECK_MODULES(JACK, jack, have_jack=yes, have_jack=no)'
  | Configure failed. The contents of all config.log files follows to aid debugging

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>