gtk-vnc looking for x11 specific symbol causes crash in virt-manager +quartz variant

[alexeijd]

opening a virtual machine that has display-vnc configured instead of display spice causes virt-manager +quartz variant to crash:

Process:               Python [55210]
Path:                  /opt/local/Library/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python
Identifier:            org.python.python
Version:               3.7.7 (3.7.7)
Code Type:             X86-64 (Native)
Parent Process:        ??? [1]
Responsible:           Terminal [697]
User ID:               501

Date/Time:             2020-06-19 10:31:46.505 +0100
OS Version:            Mac OS X 10.15.5 (19F101)
Report Version:        12
Anonymous UUID:        69566D67-1B3C-03AC-D106-8FB436B0C83E

Sleep/Wake UUID:       DCF97D95-A796-42FC-A7A8-EB68A13C47FB

Time Awake Since Boot: 760000 seconds

System Integrity Protection: enabled

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Termination Reason:    DYLD, [0x4] Symbol missing

Application Specific Information:
crashed on child side of fork pre-exec

Dyld Error Message:
  Symbol not found: _gdk_x11_display_get_type
  Referenced from: /opt/local/lib/libgtk-vnc-2.0.0.dylib
  Expected in: /opt/local/lib/libgdk-3.0.dylib