qt5: fix PIE. Closes #4314.

Adapted from Gentoo.

srcpkgs/qt5/template

@@ -1,7 +1,7 @@
 # Template file for 'qt5'
 pkgname=qt5
 version=5.6.0
-revision=9
+revision=10
 wrksrc="qt-everywhere-opensource-src-${version}"
 homepage="http://qt.io/"
 short_desc="A cross-platform application and UI framework (QT5)"
@@ -90,6 +90,10 @@ pre_configure() {
 			sed -i ${config} -e "s;HAVE_SYSCTL 1;HAVE_SYSCTL 0;"
 		done
 	esac
+	# qmake CFLAGS/LDFLAGS
+	sed -i -e '/outpath\/qmake\".*\"\$MAKE\")/s/)/ QMAKE_CFLAGS="$CFLAGS" QMAKE_CXXFLAGS="$CXXFLAGS" QMAKE_LFLAGS="$LDFLAGS" )/' \
+		-e 's/\(setBootstrapVariable\s\+\|EXTRA_C\(XX\)\?FLAGS=.*\)QMAKE_C\(XX\)\?FLAGS_\(DEBUG\|RELEASE\).*/:/' \
+		qtbase/configure
 }
 do_configure() {
 	export LD="$CXX"