Enable building the DUMM Ruby extension in a VPATH build.

configure.in

@@ -1246,6 +1246,7 @@ AC_OUTPUT(
 	src/openac/Makefile
 	src/scepclient/Makefile
 	src/dumm/Makefile
+	src/dumm/ext/extconf.rb
 	src/libfast/Makefile
 	src/manager/Makefile
 	src/medsrv/Makefile

src/dumm/ext/extconf.rb

@@ -1,21 +0,0 @@
-#
-# DUMM for Ruby
-#
-
-require "mkmf"
-
-dir_config("dumm")
-
-unless find_header('library.h', '../../libstrongswan') and
-       find_header('dumm.h', '..')
-  puts "... failed: one or more header files not found!"
-  exit
-end
-
-unless find_library('dumm', 'dumm_create')
-  puts "... failed: 'libdumm' not found!"
-  exit
-end
-
-create_makefile("dumm")
-

src/dumm/ext/extconf.rb.in

@@ -0,0 +1,18 @@
+#
+# DUMM for Ruby
+#
+
+require 'mkmf'
+
+$defs << " @DEFS@"
+
+dir_config('dumm', '@top_srcdir@/src/dumm', '../.libs')
+dir_config('strongswan', '@top_srcdir@/src/libstrongswan', '../../libstrongswan/.libs')
+
+unless find_library('dumm', 'dumm_create')
+  puts "... failed: 'libdumm' not found!"
+  exit
+end
+
+create_makefile('dumm', '@top_srcdir@/src/dumm/ext')
+