mac debugger hangs with "class/union/struct element type DIE <hex> that is a forward declaration"

with 100% reliability, on my large project, the debugger will hang, with the "Locals" view showing a "wagonwheel" animated overlay. 

this shows in debugger log:

ERROR: Lldb stderr: error: <whatever_file>.o DWARF DW_TAG_array_type DIE at <some hex> has a class/union/struct element type DIE <more hex> that is a forward declaration, not a complete definition.
Try compiling the source file with -fstandalone-debug or disable -gmodules

things i tried:

• turn off "load .gdbinit"
• turn off "load system GDB pretty printers"
• turn off "use dynamic object type for display"
• turn off "use debugging helper"
• turn off "Show QObject names if available"
• setting kit LLDB to the one inside xcode, instead of the one in /usr/bin/lldb
• setting kit compiler to "Apple Clang x86_64"
• QMAKE_CXXFLAGS_DEBUG += -fstandalone-debug
• QMAKE_CXXFLAGS_DEBUG += -fno-limit-debug-info 
• adding/removing "Qt Creator" to/from system prefs->security & privacy->privacy->accessibility
• adding/removing "source code + debug symbols" using MaintenanceTool

see this forum post for further details.

i do not know how to "disable -gmodules"

building Qt from source, to get "debug libraries" is NOT a solution, this should work out of the box.