Show error messages from DebugSymbols DBGShellCommand agent

The DebugSymbols DBGShellsCommand, which can find the symbols
for binaries, has a mechanism to return error messages when
it cannot find a symbol file.  Those errors were not printed
to the user for several corefile use case scenarios; this
patch fixes that.

Also add dyld/process logging for the LC_NOTE metadata parsers
in ObjectFileMachO, to help in seeing what lldb is basing its
searches on.

Differential Revision: https://reviews.llvm.org/D157160