apr: Cache configure tests which use AC_TRY_RUN

AC_TRY_RUN macro means the test needs to run to find the result and we
are cross compiling so this will always get wrong results, this results
in miscompiling apache2 on musl because it disables rlimit
(ac_cv_struct_rlimit) wrongly.

All these variables are determined with AC_TRY_RUN checks

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>