8230758: ZGC: Add missing precompiled include and fix friend declaration

Reviewed-by: tschatzl, pliden

src/hotspot/share/gc/z/zForwardingEntry.hpp

@@ -46,7 +46,7 @@
 //
 
 class ZForwardingEntry {
-  friend struct PrimitiveConversions;
+  friend class PrimitiveConversions;
 
 private:
   typedef ZBitField<uint64_t, bool,   0,   1> field_populated;

src/hotspot/share/gc/z/zNUMA.cpp

@@ -21,6 +21,7 @@
  * questions.
  */
 
+#include "precompiled.hpp"
 #include "gc/z/zNUMA.hpp"
 #include "logging/log.hpp"
 #include "runtime/os.hpp"