Defaults default to libdir and includedir

m4/check-package.m4

@@ -9,12 +9,19 @@ dnl $2: library name (base name, lib$2[.so|.a]
 dnl $3: library path (-L$3)
 dnl $4: additional libraries needed (e.g. -lm -lGL)
 dnl $5: header name
-dnl $6: include path (-I$6
+dnl $6: include path (-I$6)
 dnl $7 \in \{optional, required\}, bail out if required, warning otherwise
 dnl
 AC_DEFUN(ALBERT_CHECK_PKG,
-[AC_ARG_WITH($1-lib,
-[  --with-$1-lib=DIR   use $1 library below directory DIR (default: $3)],
+[AC_REQUIRE([AC_SET_PREFIX])
+if test -z "$3"; then
+	DEFAULT_LIBDIR=${libdir}
+else
+	DEFAULT_LIBDIR=$3
+fi
+AC_ARG_WITH($1-lib,
+[  --with-$1-lib=DIR   use $1 library below directory DIR
+                      (default: $DEFAULT_LIBDIR)],
 [case "$withval" in
     yes) AC_MSG_ERROR("option \"--with-$1-lib\" requires an argument")
 	;;
@@ -23,10 +30,18 @@ AC_DEFUN(ALBERT_CHECK_PKG,
     *) $1_DIR=$withval
 	;;
 esac],
-$1_DIR=$3)
+$1_DIR=$DEFAULT_LIBDIR)
+dnl
+dnl now for the header file
+dnl
+if test -z "$6"; then
+	DEFAULT_INCDIR=${libdir}
+else
+	DEFAULT_INCDIR=$6
+fi
 AC_ARG_WITH($1-headers,
 [  --with-$1-headers=DIR   use $1 include files below directory DIR
-                          (default: $6)],
+                          (default: $DEFAULT_INCDIR)],
 [case "$withval" in
     yes) AC_MSG_ERROR("option \"--with-$1-headers\" requires an argument")
 	;;
@@ -35,7 +50,7 @@ AC_ARG_WITH($1-headers,
     *) $1_INCS=$withval
 	;;
 esac],
-$1_INCLUDES=$6)
+$1_INCLUDES=$DEFAULT_INCDIR)
 dnl
 dnl now check if the library and header files exist
 dnl