Add j9cfg.h to pick up JAVA_SPEC_VERSION definition

GetModule API is guarded by JAVA_SPEC_VERSION check
that requires j9cfg.h from the 'include' directory.
Add that directory for j9vm31 compiles.  This directory
needs to be placed after include31, to ensure the correct
jni headers are used.

Signed-off-by: Joran Siu <joransiu@ca.ibm.com>

runtime/j9vm31/j9vm31.h

@@ -29,6 +29,7 @@
 
 #include "j9cel4ro64.h"
 #include "jni.h"
+#include "j9cfg.h"
 
 /* High tag bits to signify 31-bit function handles that are passed to 64-bit. */
 #define HANDLE31_HIGHTAG 0x31000000

runtime/j9vm31/module.xml

@@ -35,6 +35,7 @@ SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-excepti
 		</exports>
 		<includes>
 			<include path="j9include31"/>
+			<include path="j9include"/>
 		</includes>
 		<makefilestubs>
 			<makefilestub data="UMA_TREAT_WARNINGS_AS_ERRORS=1"/>