build: Only use PKG_INSTALLDIR if available

It's only in pkg-config 0.27 or newer, but 0.25 at least is still
fairly widespread.

diff --git a/configure.ac b/configure.ac
index d7e4ed1..4996b79 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -68,7 +68,7 @@ AC_LIBTOOL_WIN32_DLL
 AM_PROG_LIBTOOL
 AC_PROG_MAKE_SET
 PKG_PROG_PKG_CONFIG
-PKG_INSTALLDIR
+m4_ifdef([PKG_INSTALLDIR], [PKG_INSTALLDIR], AC_SUBST([pkgconfigdir], ${libdir}/pkgconfig))
 
 AC_MSG_CHECKING([for RM macro])
 _predefined_rm=`make -p -f /dev/null 2>/dev/null|grep '^RM ='|sed -e 's/^RM = //'`