[build] first pass at multiarch support

Changing bonnibel to respect the --arch flag to configure. This requires
some reworking of modules, mostly in the addition of the ModuleList
class instead of just a dict of modules.

src/kernel/kernel.module

@@ -3,7 +3,7 @@
 kernel = module("kernel",
     default = True,
     basename = "jsix",
-    targets = [ "kernel" ],
+    target = "kernel",
     description = "jsix kernel",
     deps = [ "util", "cpu", "bootproto", "j6", "acpi" ],
     static = True,

src/kernel/panic.serial/serial.module

@@ -1,7 +1,7 @@
 # vim: ft=python
 
 panic = module("panic.serial",
-    targets = [ "kernel" ],
+    target = "kernel",
     deps = [ "util", "elf", "kernel" ],
     static = True,
     includes = [ ".." ],