fuzzgen: Generate compiler flags (#5020)

* fuzzgen: Test compiler flags

* cranelift: Generate `all()` function for all enum flags

This allows a user to iterate all flags that exist.

* fuzzgen: Minimize regalloc_checker compiles

* fuzzgen: Limit the amount of test case inputs

* fuzzgen: Add egraphs flag

It's finally here! 🥳

* cranelift: Add fuzzing comment to settings

* fuzzgen: Add riscv64

* fuzzgen:  Unconditionally enable some flags

cranelift/codegen/meta/src/gen_settings.rs

@@ -98,6 +98,26 @@ fn gen_iterator(group: &SettingGroup, fmt: &mut Formatter) {
     fmtln!(fmt, "}");
 }
 
+/// Generates a `all()` function with all options for this enum
+fn gen_enum_all(name: &str, values: &[&'static str], fmt: &mut Formatter) {
+    fmtln!(
+        fmt,
+        "/// Returns a slice with all possible [{}] values.",
+        name
+    );
+    fmtln!(fmt, "pub fn all() -> &'static [{}] {{", name);
+    fmt.indent(|fmt| {
+        fmtln!(fmt, "&[");
+        fmt.indent(|fmt| {
+            for v in values.iter() {
+                fmtln!(fmt, "Self::{},", camel_case(v));
+            }
+        });
+        fmtln!(fmt, "]");
+    });
+    fmtln!(fmt, "}");
+}
+
 /// Emit Display and FromStr implementations for enum settings.
 fn gen_to_and_from_str(name: &str, values: &[&'static str], fmt: &mut Formatter) {
     fmtln!(fmt, "impl fmt::Display for {} {{", name);
@@ -158,6 +178,12 @@ fn gen_enum_types(group: &SettingGroup, fmt: &mut Formatter) {
         });
         fmtln!(fmt, "}");
 
+        fmtln!(fmt, "impl {} {{", name);
+        fmt.indent(|fmt| {
+            gen_enum_all(&name, values, fmt);
+        });
+        fmtln!(fmt, "}");
+
         gen_to_and_from_str(&name, values, fmt);
     }
 }