Initial libjit skeleton.

Not currently generating instructions, but most of the flow is right up to
that point. A lot of work required to refactor the emitter, but wanted to
get this checked in.

src/xenia/cpu/sdb/sources.gypi

@@ -7,6 +7,8 @@
     'symbol.h',
     'symbol_database.cc',
     'symbol_database.h',
+    'symbol_table.cc',
+    'symbol_table.h',
     'xex_symbol_database.cc',
     'xex_symbol_database.h',
   ]