saturating arithmetic builtins: add, sub, mul, shl (#9619)

- adds 1 simple behavior tests for each
  which does integer and vector ops at
  runtime and comptime
- adds bigint_*_sat() methods for each

- use CreateIntrinsic() which accepts a
  variable number of arguments to pass
  the scale parameter

* update langref
- added case to test/compile_errors.zig given floats

- explain upstream bug in llvm.smul.fix.sat and link to #9643 in langref and commented out test cases

* sat-arithmetic: skip mul tests if arch == .wasm32 because ci is erroring with 'LLVM ERROR: Unable to expand fixed point multiplication' when compiling for wasm32

test/compile_errors.zig

@@ -8838,4 +8838,12 @@ pub fn addCases(ctx: *TestContext) !void {
         "tmp.zig:2:9: note: declared mutable here",
         "tmp.zig:3:12: note: crosses namespace boundary here",
     });
+
+    ctx.objErrStage1("Issue #9619: saturating arithmetic builtins should fail to compile when given floats",
+        \\pub fn main() !void {
+        \\    _ = @addWithSaturation(@as(f32, 1.0), @as(f32, 1.0));
+        \\}
+    , &[_][]const u8{
+        "error: invalid operands to binary expression: 'f32' and 'f32'",
+    });
 }