configure: Fix detection of libdir in ldconfig configuration

configure: Fix detection of libdir in ldconfig configuration

Ever since commit b4b5e9ce4dac62111ec11da6d22b7e618056801f the
detection of libdir in the ldconfig configuration has been broken,
resulting in RPATH being set when not needed and not wanted.

The cause was a change from an IFS setting of:

	IFS="$(printf '\n\t')"

to a new setting of:

	IFS="$(printf '\n')"

That looks desirable since we want to split the output of ldconfig
based on newlines, (and not split on any filename that might have an
embedded tab in it). The subtle bug in the above is that the shell
trims any trailing newlines when performing command substitution so
the final statement above was equivalent to:

	IFS=''

which prevented any splitting of the ldconfig output at all.

Fix this by avoiding command substitution and just using a literal
newline in the source file for setting this variable.