configure: disallow spaces and colons in source path and build path

The configure script breaks when the qemu source directory is in a path
containing white spaces, in particular the list of targets is not
correctly generated when calling "./configure --help" because of how the
default_target_list variable is built.

In addition to that, *building* qemu from a directory with spaces breaks
some assumptions in the Makefiles, even if the original source path does
not contain spaces like in the case of an out-of-tree build, or when
symlinks are involved.

To avoid these issues, refuse to run the configure script and the
Makefile if there are spaces or colons in the source path or the build
path, taking as inspiration what the kbuild system in linux does.

Buglink: https://bugs.launchpad.net/qemu/+bug/1817345



Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Antonio Ospite <antonio.ospite@collabora.com>
Message-Id: <20190526144747.30019-3-ao2@ao2.it>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>