patch 8.2.2809: Vim9: :def function compilation fails when using :legacy

Problem:    Vim9: :def function compilation fails when using :legacy.
Solution:   Reset CMOD_LEGACY when compiling a function. (closes #8137)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 230de20..5bfad6b 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -2167,10 +2167,20 @@
 
 def Test_legacy_lambda()
   legacy echo {x -> 'hello ' .. x}('foo')
+
   var lines =<< trim END
       echo {x -> 'hello ' .. x}('foo')
   END
   CheckDefAndScriptFailure(lines, 'E720:')
+
+  lines =<< trim END
+      vim9script
+      def Func()
+        echo (() => 'no error')()
+      enddef
+      legacy call s:Func()
+  END
+  CheckScriptSuccess(lines)
 enddef
 
 def DoFilterThis(a: string): list<string>
diff --git a/src/version.c b/src/version.c
index 4b0b1cc..d235e94 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2809,
+/**/
     2808,
 /**/
     2807,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index a3154c3..8589cec 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -8767,6 +8767,7 @@
     int		ret = FAIL;
     sctx_T	save_current_sctx = current_sctx;
     int		save_estack_compiling = estack_compiling;
+    int		save_cmod_flags = cmdmod.cmod_flags;
     int		do_estack_push;
     int		new_def_function = FALSE;
 #ifdef FEAT_PROFILE
@@ -8811,6 +8812,9 @@
     current_sctx = ufunc->uf_script_ctx;
     current_sctx.sc_version = SCRIPT_VERSION_VIM9;
 
+    // Don't use the flag from ":legacy" here.
+    cmdmod.cmod_flags &= ~CMOD_LEGACY;
+
     // Make sure error messages are OK.
     do_estack_push = !estack_top_is_ufunc(ufunc, 1);
     if (do_estack_push)
@@ -9403,6 +9407,7 @@
 
     current_sctx = save_current_sctx;
     estack_compiling = save_estack_compiling;
+    cmdmod.cmod_flags =	save_cmod_flags;
     if (do_estack_push)
 	estack_pop();