Use the target-lexicon crate.

This switches from a custom list of architectures to use the
target-lexicon crate.

 - "set is_64bit=1; isa x86" is replaced with "target x86_64", and
   similar for other architectures, and the `is_64bit` flag is removed
   entirely.

 - The `is_compressed` flag is removed too; it's no longer being used to
   control REX prefixes on x86-64, ARM and Thumb are separate
   architectures in target-lexicon, and we can figure out how to
   select RISC-V compressed encodings when we're ready.

lib/simplejit/src/backend.rs

@@ -10,6 +10,7 @@ use libc;
 use memory::Memory;
 use std::ffi::CString;
 use std::ptr;
+use target_lexicon::PointerWidth;
 #[cfg(windows)]
 use winapi;
 
@@ -173,10 +174,10 @@ impl<'simple_jit_backend> Backend for SimpleJITBackend {
             }
         }
 
-        let reloc = if self.isa.flags().is_64bit() {
-            Reloc::Abs8
-        } else {
-            Reloc::Abs4
+        let reloc = match self.isa.triple().pointer_width().unwrap() {
+            PointerWidth::U16 => panic!(),
+            PointerWidth::U32 => Reloc::Abs4,
+            PointerWidth::U64 => Reloc::Abs8,
         };
         let mut relocs = Vec::new();
         for &(offset, id) in function_relocs {

lib/simplejit/src/lib.rs

@@ -18,6 +18,7 @@ extern crate cretonne_native;
 extern crate errno;
 extern crate libc;
 extern crate region;
+extern crate target_lexicon;
 
 #[cfg(target_os = "windows")]
 extern crate winapi;