Fix optimizer interfering with some native subs

When a native sub has only native arguments and is declared as "is native"
without args (i.e. already loaded library like libc) and has a very simple
function body like {} or { * } but not { ... } or other stub markers, the
optimizer could statically inline the original function body, circumventing
the call to the native function.

Mark all native subs as soft, to prevent static inlining.
Fixes GH #3244

lib/NativeCall.pm6

@@ -592,6 +592,8 @@ our role Native[Routine $r, $libname where Str|Callable|List|IO::Path|Distributi
         nqp::bindattr(self, Code, '$!do', $do);
         nqp::setcodename($do, $!name);
     }
+
+    method soft(--> True) {} # prevent inlining of the original function body
 }
 
 multi sub postcircumfix:<[ ]>(CArray:D \array, $pos) is raw is export(:DEFAULT, :types) is default {

t/04-nativecall/00-misc.t

@@ -5,7 +5,7 @@ use Test::Helpers;
 use CompileTestLib;
 compile_test_lib '00-misc';
 
-plan 3;
+plan 4;
 
 { # https://github.com/rakudo/rakudo/issues/3235
     role Foo {
@@ -15,13 +15,19 @@ plan 3;
         }
     };
 
-    is Foo.test, 3;
+    is Foo.test, 3, "body of a native sub declared in a role body replaced";
 
     my &NCstrlen := BEGIN {
         sub NCstrlen(Str --> int32) is native('./00-misc') { !!! };
     };
 
-    is NCstrlen('123'), 3;
+    is NCstrlen('123'), 3, "body of a native sub declared in a BEGIN block replaced";
+}
+
+unless $*DISTRO.is-win { # https://github.com/rakudo/rakudo/issues/3244
+    # Test needs native arguments, an "is native" without args and an empty body
+    sub abs(int32 --> int32) is native {};
+    is abs(-1), 1, "optimizer doesn't inline the native sub's original body";
 }
 
 { # https://github.com/rakudo/rakudo/issues/1576
@@ -37,3 +43,5 @@ plan 3;
         :compiler-args[«-I "$dir.absolute()" -MFoo»], :out("3\n5\n7\n9\n"),
     'no segfaults when using NC routine after using it during precomp';
 }
+
+# vim:ft=perl6