src/mumble/mumble.pro: use PKG_CONFIG instead of hardcoding call to pkg-config
src/mumble/mumble.pro: use PKG_CONFIG instead of hardcoding call to pkg-config

Patch supplied by Helmut Grohne <helmut@subdivi.de> in Debian bug #919453
https://bugs.debian.org/919453

Use set variable PKG_CONIFG to allow calling the pkg-config for the
architecture supplied in the build environment to allow cross building.

Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble