OpenSSH_6.0p1 - configure: WARNING: zlib.h: present but cannot be compiled

[Tom Nielsen]

Hello,
          I am having difficulty upgrading OpenSSH_6.0p1 to any higher version from OpenSSH_6.1p1 to OpenSSH_7.6p1. I keep getting the same error below:
Any thoughts or concerns? Am I missing something here.

Thanks in advance,

checking zlib.h usability... no
checking zlib.h presence... yes
configure: WARNING: zlib.h: present but cannot be compiled
configure: WARNING: zlib.h:     check for missing prerequisite headers?
configure: WARNING: zlib.h: see the Autoconf documentation
configure: WARNING: zlib.h:     section "Present But Cannot Be Compiled"
configure: WARNING: zlib.h: proceeding with the compiler's result
configure: WARNING:     ## ------------------------------------------- ##
configure: WARNING:     ## Report this to openssh-unix-dev at mindrot.org<mailto:openssh-unix-dev at mindrot.org> ##
configure: WARNING:     ## ------------------------------------------- ##
checking for zlib.h... no
configure: error: *** zlib.h missing - please install first or check config.log ***


ssh -V
OpenSSH_6.0p1, OpenSSL 1.0.2j  26 Sep 2016

find / -name zlib.h
/opt/freeware/include/zlib.h
/usr/include/zlib.h
/usr/local/include/zlib.h