doc/link.md: update mruby-config description.

doc/guides/compile.md

@@ -527,7 +527,9 @@ convenience. `mruby-config` command prints the configuration used for `libmruby.
 $ mruby-config --help
 Usage: mruby-config [switches]
   switches:
+  --cc                        print compiler name
   --cflags                    print flags passed to compiler
+  --ld                        print linker name
   --ldflags                   print flags passed to linker
   --ldflags-before-libs       print flags passed to linker before linked libraries
   --libs                      print linked libraries

doc/guides/link.md

@@ -49,7 +49,10 @@ for example:
 * `-D` to specify mruby configuration macros
 
 To retrieve compiler options used to build `mruby`, you can use `mruby-config`
-command.
+command with following options:
+
+* `--cc`                    compiler name
+* `--cflags`                options passed to compiler
 
 ```
 $ mruby-config --cflags
@@ -63,6 +66,7 @@ compatible to mruby configuration.
 
 To retrieve linker options, you can use `mruby-config` with following options:
 
+* `--ld`                    linker name
 * `--ldflags`               options passed to linker
 * `--ldflags-before-libs`   options passed to linker before linked libraries
 * `--libs`                  linked libraries