define USE_HEAPALLOC in gssapi_alloc.h

Easier to disable for testing.

Signed-off-by: Kevin Wasserman <kevin.wasserman@painless-security.com>

https://github.com/krb5/krb5/commit/c8cd6bd75776de265e34bc2dae9b3fd234759126
Author: Kevin Wasserman <kevin.wasserman@painless-security.com>
Committer: Sam Hartman <hartmans@mit.edu>
Commit: c8cd6bd75776de265e34bc2dae9b3fd234759126
Branch: master
 src/lib/gssapi/generic/gssapi_alloc.h |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)