Can't use pg_config to look up directories when cross-compiling

  DQT_NO_DEBUG -DQT_PLUGIN -DQT_GUI_LIB -DQT_CORE_LIB -I. -I../../../../include -I../../../../include/QtGui -I../../../../include/QtCore -I.moc -I/home/qt/openssl-1.0.2/include -I../../../../mkspecs/android-clang -o .obj/moc_main.o .moc/moc_main.cpp 
agent:2019/01/31 10:26:26 build.go:192: 12 warnings and 11 errors generated.  
agent:2019/01/31 10:26:26 build.go:192: make[4]: *** [.obj/qsql_psql.o] Error 1  
agent:2019/01/31 10:26:26 build.go:192: make[4]: Leaving directory `/home/qt/work/qt/qtbase/src/plugins/sqldrivers/psql'
agent:2019/01/31 10:26:26 build.go:192: make[3]: *** [sub-psql-make_first] Error 2
agent:2019/01/31 10:26:26 build.go:192: make[3]: Leaving directory `/home/qt/work/qt/qtbase/src/plugins/sqldrivers'
agent:2019/01/31 10:26:26 build.go:192: make[2]: *** [sub-sqldrivers-make_first] Error 2
agent:2019/01/31 10:26:26 build.go:192: make[2]: *** Waiting for unfinished jobs....