build: gh27 Allow builds in paths with spaces

build: gh27 Allow builds in paths with spaces

Add quotes around shell var expansions in the update_external_sources scripts.

For Windows, remove the cmake directives to add a linker option for the DEF
files.  These were redundant with the DEF files getting added via the
cmake add_library() directive.  They were also causing difficult-to-fix
problems with paths that have spaces in them.

Change-Id: I741bac31bbf27deae59031b6aa916c6ab48383a6