Support 32 bit and 64 bit decoding with one binary

It is possible to configure the build process such that decoding of 32
bit and 64 bit instructions can be chosen at runtime using an additional
parameter of the decode function. The header file is now entirely
architecture-independent and no longer required any previous defines.

Decoding x86-64 still requires a 64-bit pointer size.

meson.build

@@ -29,13 +29,21 @@ if get_option('warning_level').to_int() >= 3
                         language: 'c')
 endif
 
+decode_32 = false
+decode_64 = false
+
 archmode = get_option('archmode')
-if archmode == '32'
+if archmode == 'only32' or archmode == 'both'
   add_project_arguments(['-DARCH_386'], language: 'c')
-elif archmode == '64'
+  decode_32 = true
+endif
+if archmode == 'only64' or archmode == 'both'
   add_project_arguments(['-DARCH_X86_64'], language: 'c')
-else
-  error('Invalid architecture mode')
+  decode_64 = true
+endif
+
+if not decode_32 and not decode_64
+  error('no architecture mode')
 endif
 
 instr_data = custom_target('tables',