Always require a Flags reference for verifying functions.

Add a settings::FlagsOrIsa struct which represents a flags reference and
optionally the ISA it belongs to. Use this for passing flags/isa
information to the verifier.

The verify_function() and verify_context() functions are now generic so
they accept either a &Flags or a &TargetISa argument.

Fix the return_at_end verifier tests which no longer require an ISA
specified. The signle "set return_at_end" flag setting now makes it to
the verifier even when no ISA is present to carry it.

cranelift/src/filetest/subtest.rs

@@ -4,7 +4,7 @@ use std::result;
 use std::borrow::Cow;
 use cretonne::ir::Function;
 use cretonne::isa::TargetIsa;
-use cretonne::settings::Flags;
+use cretonne::settings::{Flags, FlagsOrIsa};
 use cton_reader::{Details, Comment};
 use filecheck::{self, CheckerBuilder, Checker, Value as FCValue};
 
@@ -29,6 +29,16 @@ pub struct Context<'a> {
     pub isa: Option<&'a TargetIsa>,
 }
 
+impl<'a> Context<'a> {
+    /// Get a `FlagsOrIsa` object for passing to the verifier.
+    pub fn flags_or_isa(&self) -> FlagsOrIsa<'a> {
+        FlagsOrIsa {
+            flags: self.flags,
+            isa: self.isa,
+        }
+    }
+}
+
 /// Common interface for implementations of test commands.
 ///
 /// Each `.cton` test file may contain multiple test commands, each represented by a `SubTest`