Qt disables all pkg-config tests if it notices itself
being cross-compiled and PKG_CONFIG_SYSROOT_DIR being
unset.
However we do have a working pkg-config (wrapper around
pkg-config.real) which fixes the issues PKG_CONFIG_SYSROOT_DIR
tries to address.
Qt tries to be too smart in our case - force it to use
pkg-config.
--- /dev/null
+--- qtbase-opensource-src-5.8.0-beta/configure.pri.orig 2016-11-20 20:06:38.811897204 +0100
++++ qtbase-opensource-src-5.8.0-beta/configure.pri 2016-11-20 20:06:54.279928752 +0100
+@@ -174,7 +174,7 @@
+ "Disabling pkg-config since PKG_CONFIG_SYSROOT_DIR is not set." \
+ "Set this variable to your sysroot for pkg-config to function correctly when" \
+ "cross-compiling or use -pkg-config to override this test.")
+- return(false)
++# return(false)
+ }
+
+ pkgConfigSysrootDir = $$sysroot