i#4156: Fix Mach-O underflow leading to assert (#4163)
i#4156: Fix Mach-O underflow leading to assert (#4163)

Fixes a Mach-O __LINKEDIT handling bug where those sections are
assumed to all be below the shared region.

Fixes: #4156 
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio