Description:
Hello, I've been experiencing crashes with FreeCAD 0.16 from Arch official. Briefly, FreeCAD crashes as soon as I switch into Arch, Drawing or Complete workbenches (all other workbenches work fine). Using the FreeCAD provided Appimage works fine, and I've confirmed that pivy/libCoin.so and libFreeCADGui.so are both using the same version of libCoin (0.60)

Some discussion on the FreeCAD forums has indicated that it is because Qt4 and Qt5 are both linked to FreeCAD whereas only one of these two is required. Please see FreeCAD dev yorik's comment here: https://forum.freecadweb.org/viewtopic.php?f=3&t=25170&p=198684#p198610

I'm attaching the gdb output that yorik quotes below.

Additional info:
$ gdb freecad

GNU gdb (GDB) 8.0.1
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from freecad...(no debugging symbols found)...done.
(gdb) run
Starting program: /usr/bin/freecad
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
FreeCAD 0.16, Libs: 0.16RUnknown
© Juergen Riegel, Werner Mayer, Yorik van Havre 2001-2015
##### #### ### ####
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# ## #### #### # # # # #
#### # # # # # # # ##### # #
# # #### #### # # # # #
# # # # # # # # # ## ## ##
# # #### #### ### # # #### ## ## ##


Program received signal SIGSEGV, Segmentation fault.
0x00007fffc8e24277 in QMetaObject::className() const ()
from /usr/lib/libQt5Core.so.5
(gdb) bt
#0 0x00007fffc8e24277 in QMetaObject::className() const ()
at /usr/lib/libQt5Core.so.5
#1 0x00007fffc9b914b0 in () at /usr/lib/libQt5Widgets.so.5
#2 0x00007fffc9b32137 in () at /usr/lib/libQt5Widgets.so.5
#3 0x00007ffff7de757a in call_init.part () at /lib64/ld-linux-x86-64.so.2
#4 0x00007ffff7de7686 in _dl_init () at /lib64/ld-linux-x86-64.so.2
#5 0x00007ffff7debb5e in dl_open_worker () at /lib64/ld-linux-x86-64.so.2
#6 0x00007ffff4afff14 in _dl_catch_error () at /usr/lib/libc.so.6
#7 0x00007ffff7deb37a in _dl_open () at /lib64/ld-linux-x86-64.so.2
#8 0x00007ffff11f3e86 in () at /usr/lib/libdl.so.2
#9 0x00007ffff4afff14 in _dl_catch_error () at /usr/lib/libc.so.6
#10 0x00007ffff11f4587 in () at /usr/lib/libdl.so.2
#11 0x00007ffff11f3f22 in dlopen () at /usr/lib/libdl.so.2
#12 0x00007ffff54ab9e1 in () at /usr/lib/libQtCore.so.4
#13 0x00007ffff54a6039 in () at /usr/lib/libQtCore.so.4
#14 0x00007ffff54a6763 in () at /usr/lib/libQtCore.so.4
#15 0x00007ffff77652cf in QFormInternal::QFormBuilder::updateCustomWidgets() ()
at /usr/lib/freecad/lib/libFreeCADGui.so
#16 0x00007ffff773b8af in QUiLoader::QUiLoader(QObject*) ()
at /usr/lib/freecad/lib/libFreeCADGui.so
#17 0x00007ffff76e975f in Gui::UiLoader::UiLoader(QObject*) ()
at /usr/lib/freecad/lib/libFreeCADGui.so
#18 0x00007ffff76e98dd in Gui::UiLoaderPy::UiLoaderPy() ()
---Type <return> to continue, or q <return> to quit---q
at /usr/lib/freecad/lQuit
(gdb) q


Steps to reproduce:
Open FreeCAD 0.16; switch into Arch/Draft/Complete workbench. Another user on the FreeCAD forum has tried and failed to reproduce the crash, perhaps as they are only using a single version of Qt.