add new demo program

jcl/DEMOPROG.jcl

@@ -0,0 +1,5 @@
+//DEMOPROG JOB (GCC),'C Program',
+//             NOTIFY=@05054,CLASS=A,MSGCLASS=A,
+//             MSGLEVEL=(1,1),REGION=4M,TIME=1440
+//STEP1 EXEC GCCCG,INFILE='@05054.SRCLIB.C(DEMOPROG)'
+//

src/DEMOPROG.c

@@ -0,0 +1,13 @@
+//
+// Created by Gregory Gauthier on 06/02/2026.
+//
+# include <stdio.h>
+
+#ifndef HELLO_STRING
+#define HELLO_STRING "This is a new Hello World!"
+#endif
+
+int main() {
+    printf("%s\n", HELLO_STRING);
+    return 0;
+}