patch 9.0.1358: compilation error with some compilers

Problem:    Compilation error with some compilers.
Solution:   Avoid using "class" as member name.
diff --git a/src/vim9.h b/src/vim9.h
index d9b25da..48751ce 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -102,7 +102,7 @@
     ISN_PUSHCHANNEL,	// push NULL channel
     ISN_PUSHJOB,	// push NULL job
     ISN_PUSHOBJ,	// push NULL object
-    ISN_PUSHCLASS,	// push class, uses isn_arg.class
+    ISN_PUSHCLASS,	// push class, uses isn_arg.classarg
     ISN_NEWLIST,	// push list from stack items, size is isn_arg.number
 			// -1 for null_list
     ISN_NEWDICT,	// push dict from stack items, size is isn_arg.number
@@ -520,7 +520,7 @@
 	channel_T	    *channel;
 	job_T		    *job;
 	partial_T	    *partial;
-	class_T		    *class;
+	class_T		    *classarg;
 	jump_T		    jump;
 	jumparg_T	    jumparg;
 	forloop_T	    forloop;