package/webrtc-audio-processing: needs host-pkgconf

configure fails if the pkgconfig.m4 macros are not available during
this package autoreconf:

./configure: line 11829: syntax error near unexpected token `GNUSTL,'
./configure: line 11829: `  PKG_CHECK_MODULES(GNUSTL, gnustl)'

Fixes:
 - http://autobuild.buildroot.org/results/9cbdfb76ea38864fce1acca88714c48c41c77255

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/webrtc-audio-processing/webrtc-audio-processing.mk

@@ -10,6 +10,7 @@ WEBRTC_AUDIO_PROCESSING_SITE = http://freedesktop.org/software/pulseaudio/webrtc
 WEBRTC_AUDIO_PROCESSING_INSTALL_STAGING = YES
 WEBRTC_AUDIO_PROCESSING_LICENSE = BSD-3-Clause
 WEBRTC_AUDIO_PROCESSING_LICENSE_FILES = COPYING
+WEBRTC_AUDIO_PROCESSING_DEPENDENCIES = host-pkgconf
 # 0001-Proper-detection-of-cxxabi.h-and-execinfo.h.patch
 WEBRTC_AUDIO_PROCESSING_AUTORECONF = YES