Using low-level parse to speed up things

Thanks to @ugexe and @taboege for hints on how to make this. I've
checked memory, and it's actually taking quite a bit of memory, but
not as much as EVAL and it's actually faster than that.

It's also producing a false positive with `class
Metamodel::ParametricRoleHOW` which I don't know how to fix.

Refs #2764 but leaves it open until

* Memory usage has actually been addressed, and
* We manage to fix that false positive

doc/Language/exceptions.pod6

@@ -392,7 +392,6 @@ converted to a normal exception.
 
 =begin code
 { return; CATCH { default { $*ERR.say: .^name, ': ',.Str } } }
-
 # OUTPUT: «X::ControlFlow::Return: Attempt to return outside of any Routine␤»
 # was CX::Return
 =end code

xt/examples-compilation.t

@@ -133,21 +133,23 @@ sub check-chunk( $eg ) {
     my $has-error;
     {
         # Does the test require its own file?
-#        if $eg<solo> {
+        if $eg<solo> {
             my ($tmp_fname, $tmp_io) = tempfile;
             $tmp_io.spurt: $code, :close;
             my $proc = Proc::Async.new($*EXECUTABLE, '-c', $tmp_fname);
             $proc.stdout.tap: {;};
             $proc.stderr.tap: {;};
             $has-error = ! await $proc.start;
-        # } else {
-        #     temp $*OUT = open :w, $*SPEC.devnull;
-        #     temp $*ERR = open :w, $*SPEC.devnull;
-        #     try EVAL $code;
-        #     $has-error = $!;
-        #     close $*OUT;
-        #     close $*ERR;
-        # }
+        } else {
+            temp $*OUT = open :w, $*SPEC.devnull;
+            temp $*ERR = open :w, $*SPEC.devnull;
+            use nqp;
+            my $*LINEPOSCACHE;
+            $has-error = not try { nqp::getcomp('perl6').parse($code) };
+            close $*OUT;
+            close $*ERR;
+
+        }
     }
 
     todo(1) if $eg<todo>;