Made IRMemoryMap::FindSpace a little cleverer,

and made attempts to allocate memory in the process
fall back to FindSpace and just allocate memory on
the host (but with real-looking pointers, hence
FindSpace) if the process doesn't allow allocation.
This allows expressions to run on processes that don't
support allocation, like core files.

This introduces an extremely rare potential problem:
If all of the following are true:

- The Process doesn't support allocation;

- the user writes an expression that refers to an
  address that does not yet map to anything, or is
  dynamically generated (e.g., the result of calling
  a function); and

- the randomly-selected address for the static data
  for that specific expression runs into the
  address the user was expecting to work with;

then dereferencing the pointer later results
in the user seeing something unexpected.  This is
unlikely but possible; as a future piece of work,
we should have processes be able to hint to the
expression parser where it can allocate temporary data
of this kind.

llvm-svn: 179827