Drop 'basic-blocks' feature (#1363)

* All: Drop 'basic-blocks' feature

This makes it so that 'basic-blocks' cannot be disabled and we can
start assuming it everywhere.

* Tests: Replace non-bb filetests with bb version

* Tests: Adapt solver-fixedconflict filetests to use basic blocks

cranelift/filetests/src/runone.rs

@@ -52,31 +52,6 @@ pub fn run(path: &Path, passes: Option<&[String]>, target: Option<&str>) -> Test
         }
     };
 
-    for feature in testfile.features.iter() {
-        let (flag, test_expect) = match feature {
-            Feature::With(name) => (name, true),
-            Feature::Without(name) => (name, false),
-        };
-        let cranelift_has = match *flag {
-            // Add any cranelift feature flag here, and make sure that it is forwarded to the
-            // cranelift-filetest crate in the top-level Cargo.toml.
-            "basic-blocks" => cfg!(feature = "basic-blocks"),
-            _ => {
-                return Err(format!(
-                    r#"{:?}: Unknown feature flag named "{}""#,
-                    path, flag
-                ))
-            }
-        };
-        if cranelift_has != test_expect {
-            println!(
-                r#"skipping test {:?}: non-matching feature flag "{}""#,
-                path, flag
-            );
-            return Ok(started.elapsed());
-        }
-    }
-
     if testfile.functions.is_empty() {
         return Err("no functions found".to_string());
     }