We introduced helper macros to simplify loading functions dynamically.
Might just as well use them.
This also side-steps a compiler warning when building with GCC v8.x: it
would complain about casting between incompatible function pointers.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>