Update to rscons 2.3.0

Move cross compiler to i686-elf-gcc directory.
Automatically build cross compiler using rscons subsidiary script.

i686-elf-gcc/Rsconscript

@@ -0,0 +1,17 @@
+configure do
+  check_c_compiler "gcc"
+  check_program "make"
+  check_program "bison"
+  check_program "flex"
+  check_program "texi2any", on_fail: "Install the texinfo package"
+  check_program "wget"
+  check_lib "gmp", on_fail: "Install the libgmp-dev package"
+  check_lib "mpc", on_fail: "Install the libmpc-dev package"
+  check_lib "mpfr", on_fail: "Install the libmpfr-dev package"
+end
+
+build do
+  unless File.exist?("i686-elf-gcc")
+    system("./build.sh")
+  end
+end