HDFFV-9994 port changes from develop.

CMake folder changes brought up to standard.

config/cmake_ext_mod/HDFCXXTests.cpp

@@ -54,3 +54,38 @@ int main(void) {
 }
 
 #endif
+
+#ifdef CXX_HAVE_OFFSETOF
+
+#include <stdio.h>
+#include <stddef.h>
+
+#ifdef FC_DUMMY_MAIN
+#ifndef FC_DUMMY_MAIN_EQ_F77
+#  ifdef __cplusplus
+extern "C"
+#  endif
+int FC_DUMMY_MAIN()
+{ return 1;}
+#endif
+#endif
+int
+main ()
+{
+
+  struct index_st
+  {
+    unsigned char type;
+    unsigned char num;
+    unsigned int len;
+  };
+  typedef struct index_st index_t;
+  int x,y;
+  x = offsetof(struct index_st, len);
+  y = offsetof(index_t, num)
+
+  ;
+  return 0;
+}
+
+#endif