build-sys: "link" libsystemd-id128.so with libsystemd-label

Fixed build on debian wheezy:
./.libs/libudev.so: undefined reference to `cg_create'

Appears to have no influence on the resulting binaries and
libraries. Cf. b5fafdf63f.
man: fix spacing issue in various man pages

Before: libsystemd-daemonpkg-config(1)
After: libsystemd-daemon pkg-config(1)

This fix is more complicated than it should be due to the consecutive
XML elements separated by collapsible whitespace.

Merging the lines and separating the XML elements with an en space or a
non-breaking space is the only solution that results in one, and only
one, space being inserted between them when testing. An em space results
in two spaces being inserted.