Use $libexecdir instead of hardcoding $prefix/lib as this breaks multilib builds.

Upstream-Status: Inappropriate
Signed-off-by: Ross Burton <ross.burton@arm.com>

diff --git a/config-scripts/cups-directories.m4 b/config-scripts/cups-directories.m4
index 1430af3a6..6efedc604 100644
--- a/config-scripts/cups-directories.m4
+++ b/config-scripts/cups-directories.m4
@@ -265,7 +265,7 @@ case "$host_os_name" in
 	*-gnu)
 		# GNUs
 		INSTALL_SYSV="install-sysv"
-		CUPS_SERVERBIN="$exec_prefix/lib/cups"
+		CUPS_SERVERBIN="$libexecdir/cups"
 		;;
 	*bsd* | darwin*)
 		# *BSD and Darwin (macOS)
@@ -275,7 +275,7 @@ case "$host_os_name" in
 	*)
 		# All others
 		INSTALL_SYSV="install-sysv"
-		CUPS_SERVERBIN="$exec_prefix/lib/cups"
+		CUPS_SERVERBIN="$libexecdir/cups"
 		;;
 esac