Do not copy glibc sources in build-many-glibcs.py.

Now that build-many-glibcs.py touches at checkout time all files that
might get rebuilt in the glibc source directory in a normal glibc
build and test run, this patch stops the script from copying the glibc
source directory, so that all builds use the original directory
directly (and less disk space is used, less I/O is involved and cached
copies of the sources in memory can be shared between all the builds -
as well as avoiding spurious failures from copying while "git gc" is
running).  This is similar to how all other components were already
handled.  Any bugs involving writing into the source directory can be
dealt with in future as normal bugs, just as such bugs already are
handled.

Tested with build-many-glibcs.py runs with a read-only glibc source
directory, with all files not touched by the script having timestamps
in forwards alphabetical order and separately with all files not
touched by the script having timestamps in backwards alphabetical
order.

	* scripts/build-many-glibcs.py (Glibc.build_glibc): Use original
	source directory instead of a copy.
	(CommandList.create_copy_dir): Remove.