Debugger: Disable dumper for QVariants with user defined types for LLDB

The type info is not directly accessible to the debugger. The workaround
used so far generally works for initialized data, but can force loading
all debug information otherwise. The behavior is exceptionally bad
for LLDB 3.7 with GCC 5.x/C++14 due DW_TAG_base_type 'auto' encoded with
DW_ATE = 0x0, bit_size = 0 produced by GCC and not understood by LLDB.

Change-Id: I2b28b8a6aa15751c8e797bcbf501b81622680596
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>