malloc: Use compat_symbol_reference in libmcheck [BZ #22050]

Since glibc 2.24, __malloc_initialize_hook is a compat symbol.  As a
result, the link editor does not export a definition of
__malloc_initialize_hook from the main program, so that it no longer
interposes the variable definition in libc.so.  Specifying the symbol
version restores the exported symbol.