Don't use -L$x_libraries 'cause $x_libraries can be empty, -L without

argument confuses the linker or resets the search path for libraries.
Instead, use AC_PATH_XTRA and $X_LIBS.

configure.ac

@@ -125,13 +125,13 @@ case "$build_os" in
 		[-lg2c])
 	AC_CHECK_LIB(X11, main,,
 		[AC_MSG_ERROR([Exiting...])],
-		[-L$x_libraries])
+		[${X_LIBS}])
 	AC_CHECK_LIB(Xext, main,,
 		[AC_MSG_ERROR([Exiting...])],
-		[-L$x_libraries])
+		[${X_LIBS}])
 	AC_CHECK_LIB(GL, main,,
 		[AC_CHECK_LIB(MesaGL,main)],
-		[-L$x_libraries])
+		[${X_LIBS}])
 ;;
 *)
 	AC_CHECK_LIB(blas, main,,                                                             
@@ -139,10 +139,10 @@ case "$build_os" in
                 make_own_blas_lib=libblas.la])
 	AC_CHECK_LIB(X11, main,,
 		[AC_MSG_ERROR(Exiting...)],
-		[-L$x_libraries])
+		[${X_LIBS}])
 	AC_CHECK_LIB(Xext, main,,
 		[AC_MSG_ERROR(Exiting...)],
-		[-L$x_libraries])
+		[${X_LIBS}])
 	AC_CHECK_LIB(gl, main)
 	AC_CHECK_LIB(GL, main)
 ;;