build: convert "echo" usage into a patch in qt package

depends/patches/qt/fix_mingw_cross_compile.patch

@@ -0,0 +1,25 @@
+commit 5a992a549adfe5a587bbcd6cd2b2cee47d236e27
+Author: fanquake <fanquake@gmail.com>
+Date:   Fri Sep 4 08:13:44 2020 +0800
+
+    Work around broken mingw cross-compilation
+
+    See upstream issues:
+    https://bugreports.qt.io/browse/QTBUG-63637
+    https://bugreports.qt.io/browse/QTBUG-63659
+    https://codereview.qt-project.org/q/8bebded9
+
+    We should be able to drop this once we are building qt 5.10.1 or later.
+
+    Added in #12971.
+
+diff --git a/qtbase/mkspecs/win32-g++/qmake.conf b/qtbase/mkspecs/win32-g++/qmake.conf
+index e071a0d1..ad229b10 100644
+--- a/qtbase/mkspecs/win32-g++/qmake.conf
++++ b/qtbase/mkspecs/win32-g++/qmake.conf
+@@ -87,3 +87,5 @@ QMAKE_NM                = $${CROSS_COMPILE}nm -P
+ include(../common/angle.conf)
+
+ load(qt_config)
++QMAKE_LINK_OBJECT_MAX = 10
++QMAKE_LINK_OBJECT_SCRIPT = object_script