Call it innocence, call it naive, call it whatever - but APR is an obstacle to be overcome. There is documentation, but lacks an overview of what/how apr is used.
X pages long list of variables does not help prepare one (read me if you will) for proper usage.

CASE: built apr, apr-util, httpd on separate system. Want to verify process used to create build on another system. Unfortunately, apr has undefined variables so cannot build in second environment - install APR and APR-UTIL packaged in previous environment. Insert extra files in /usr/include same as on original system.

Start configure - runs well until zlib is needed (copy files to /usr/include, per above and compile conftest.c successfully). Run configure again, still fails.
My guess, after looking at the log output is that while /usr/include/zlib.h was found and used on the original system now "configure" is only using the /opt/include
where the files are not located.

Request: please think about the basic documentation - right now if you follow the documentation link the first page is one that seems to be "there is no documentation".
The other navigation items show otherwise - but what are all these functions, modules, etc. And how do they explain that configure does not work.

p.s. the first hint that something was wrong was the return of a static name for a compiler (was cc - xlc was better), but now working with gcc - so everything fails.
-- I have learned that apr and apr-util are largely static - executable caching of variables - is that one way of describing how it works?

Note: I have no idea of what is in libapr or libaprutil - but I am concerned that they are not going to be portable enough to use across different hardware/os platforms
even those platforms are binary compatible. Also - maybe - the problems are limited to apr-1-config and apu-1-config. Here is hoping!

Note: 6000-ibm-aix: bad number ... Is this because this is an AIX 7.1 system? It moves on, thankfully, but thought this was the cause initially.

======
./configure[5865]: 6000-ibm-aix: bad number
+ cp conftest.c mytest.c
+ ac_fn_c_try_link 11027
+ print -r -- configure:11035: result: not found
+ 1>& 5
+ print -r -- not found
+ 1>& 6
+ enable_deflate=no
+ INCLUDES=-I$(top_builddir)/srclib/pcre -I. -I$(top_srcdir)/os/$(OS_DIR) -I$(top_srcdir)/server/mpm/$(MPM_SUBDIR_NAME) -I$(top_srcdir)/modules/http -I$(top_srcdir)/modules/filters -I$(top_srcdir)/modules/proxy -I$(top_srcdir)/include -I$(top_srcdir)/modules/generators -I$(top_srcdir)/modules/mappers -I$(top_srcdir)/modules/database -I/opt/include -I/usr/include/openssl/include
+ LDFLAGS=  -L/usr/include/openssl/lib
+ rm -f core conftest.err conftest.o conftest conftest.c
+ test x-lm  -lz = x-lz
+ apr_new_bugger=
+ apr_removed=0
+ test x-lm != x-lz
+ apr_new_bugger= -lm
+ test x-lz != x-lz
+ apr_removed=1
+ test 1 = 1
+ test x != xyes
+ echo   removed "-lz" from LIBS
+ LIBS= -lm
+ CPPFLAGS=
+ print -r -- configure:11066: checking whether to enable mod_deflate
+ 1>& 5
+ print -rn -- checking whether to enable mod_deflate...
+ 1>& 6
+ test no = no
+ test yes = no
+ as_fn_error mod_deflate has been requested but can not be built due to prerequisite failures 11072 5
configure: error: mod_deflate has been requested but can not be built due to prerequisite failures
+ exit_status=1
+ 1>& 5
=======