* configure.in (doug_lea_malloc): Check for __malloc_initialize_hook.

* configure.in (doug_lea_malloc): Check for __malloc_initialize_hook.

With glibc 2.14 or later, when compiled with GCC 4.7.0's
-Werror=deprecated-declarations flag, use of hooks like
__malloc_initialize_hook causes compilation to fail because these
hooks are deprecated.  Modify 'configure' to check for these hooks too.
Simplify the 'configure' code to test for all the hooks at once.
(emacs_cv_var___after_morecore_hook): Remove, replacing with ...
(emacs_cv_var_doug_lea_malloc): ... this new var.