Solves issue with trying to locate icudtl.dat in /usr/share/qt5/ when built
with system-icu.

Patch from Fedora.

--- a/src/core/config/linux.pri
+++ b/src/core/config/linux.pri
@@ -40,6 +40,6 @@
 use?(system_snappy):   GYP_CONFIG += use_system_snappy=1
 use?(system_speex):    GYP_CONFIG += use_system_speex=1
 use?(system_vpx):      GYP_CONFIG += use_system_libvpx=1
-use?(system_icu):      GYP_CONFIG += use_system_icu=1
+use?(system_icu):      GYP_CONFIG += use_system_icu=1 icu_use_data_file_flag=0
 use?(system_ffmpeg):   GYP_CONFIG += use_system_ffmpeg=1