FE 1.0: Make 'suspend fun', where 'suspend' is not builtin error in 1.8

#KT-49264 Fixed

compiler/testData/diagnostics/tests/coroutines/modifierFormBuiltinSuspendFun.kt

@@ -0,0 +1,11 @@
+// LANGUAGE: +ModifierNonBuiltinSuspendFunError
+// FIR_IDENTICAL
+// SKIP_TXT
+
+infix fun Int.suspend(c: () -> Unit) {}
+
+fun foo() {
+    1 <!MODIFIER_FORM_FOR_NON_BUILT_IN_SUSPEND_FUN_ERROR!>suspend<!> fun () {}
+
+    1.suspend(fun () {})
+}