Implement reloc_names() for all targets.

This gets rid of the last TargetIsa method with a default
implementation.

lib/cretonne/src/isa/arm32/binemit.rs

@@ -4,3 +4,5 @@ use binemit::{CodeSink, bad_encoding};
 use ir::{Function, Inst};
 
 include!(concat!(env!("OUT_DIR"), "/binemit-arm32.rs"));
+
+pub static RELOC_NAMES: [&'static str; 1] = ["Call"];

lib/cretonne/src/isa/arm32/mod.rs

@@ -94,4 +94,8 @@ impl TargetIsa for Isa {
     fn emit_inst(&self, func: &ir::Function, inst: ir::Inst, sink: &mut CodeSink) {
         binemit::emit_inst(func, inst, sink)
     }
+
+    fn reloc_names(&self) -> &'static [&'static str] {
+        &binemit::RELOC_NAMES
+    }
 }

lib/cretonne/src/isa/arm64/binemit.rs

@@ -4,3 +4,5 @@ use binemit::{CodeSink, bad_encoding};
 use ir::{Function, Inst};
 
 include!(concat!(env!("OUT_DIR"), "/binemit-arm64.rs"));
+
+pub static RELOC_NAMES: [&'static str; 1] = ["Call"];

lib/cretonne/src/isa/arm64/mod.rs

@@ -87,4 +87,8 @@ impl TargetIsa for Isa {
     fn emit_inst(&self, func: &ir::Function, inst: ir::Inst, sink: &mut CodeSink) {
         binemit::emit_inst(func, inst, sink)
     }
+
+    fn reloc_names(&self) -> &'static [&'static str] {
+        &binemit::RELOC_NAMES
+    }
 }

lib/cretonne/src/isa/mod.rs

@@ -210,7 +210,5 @@ pub trait TargetIsa {
     ///
     /// This array can be indexed by the contents of `binemit::Reloc` objects passed to a
     /// `CodeSink`.
-    fn reloc_names(&self) -> &'static [&'static str] {
-        unimplemented!()
-    }
+    fn reloc_names(&self) -> &'static [&'static str];
 }