If the user has specified target.memory-module-load-level 'minimal'

and we couldn't find a dyld binary on the debug system, override
that setting and read dyld out of memory - we need to put an
internal breakpoint on dyld to register binaries being loaded or
unloaded; the debugger won't work right without dyld symbols.

<rdar://problem/27857025> 

llvm-svn: 279704