To enable Dynamic Allocation Functions, features from ISO/IEC TR 24731-2:2010,
the macro __STDC_WANT_LIB_EXT2__ hs to be defined to 1 before to the stdio.h
header is included.

--- a/src/H5private.h
+++ b/src/H5private.h
@@ -25,6 +25,8 @@
  * implicitly. */
 #define __STDC_WANT_IEC_60559_TYPES_EXT__
 
+#define __STDC_WANT_LIB_EXT2__ 1  // define for TR 24731-2:2010 extensions (e.g., vasprintf)
+
 #include "H5public.h" /* Include Public Definitions    */
 
 #include <assert.h>