We built the 7.3.1 archive 4 days ago, and it is complaining about the header file memcached.hhttps://travis-ci.org/travis-ci/php-src-builder/jobs/490240941#L5230. It appears that ./configure did not (does not?) exit with nonzero status upon error, so we continued with the rest of the build.
Could you try specifying 7.3.0 to see if that works for you?
Just to post a +1 complaint… we had to revert to Trusty as a quick fix to stop all builds from failing, and we’re hesitant to add a workaround for PECL installation.
Warning: PHP Startup: Unable to load dynamic library ‘/home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so’ - /home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so: cannot open shared object file: No such file or directory in Unknown on line 0
PHP Warning: PHP Startup: Unable to load dynamic library ‘/home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so’ - /home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so: cannot open shared object file: No such file or directory in Unknown on line 0
Warning: PHP Startup: Unable to load dynamic library ‘/home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so’ - /home/travis/.phpenv/versions/7.0.25/lib/php/extensions/no-debug-zts-20151012/memcache.so: cannot open shared object file: No such file or directory in Unknown on line 0
You are using Trusty, with an old PHP 7.0.25 binary that was compiled on October 26 2017. You should move to Xenial and/or Try a different, newer version of PHP.
Warning: PHP Startup: Unable to load dynamic library ‘memcache.so’ (tried: /home/travis/.phpenv/versions/7.3.9/lib/php/extensions/no-debug-zts-20180731/memcache.so (/home/travis/.phpenv/versions/7.3.9/lib/php/extensions/no-debug-zts-20180731/memcache.so: cannot open shared object file: No such file or directory), /home/travis/.phpenv/versions/7.3.9/lib/php/extensions/no-debug-zts-20180731/memcache.so.so (/home/travis/.phpenv/versions/7.3.9/lib/php/extensions/no-debug-zts-20180731/memcache.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
Warning: PHP Startup: Unable to load dynamic library ‘memcache.so’ (tried: /home/travis/.phpenv/versions/7.3.11/lib/php/extensions/no-debug-zts-20180731/memcache.so (/home/travis/.phpenv/versions/7.3.11/lib/php/extensions/no-debug-zts-20180731/memcache.so: cannot open shared object file: No such file or directory), /home/travis/.phpenv/versions/7.3.11/lib/php/extensions/no-debug-zts-20180731/memcache.so.so (/home/travis/.phpenv/versions/7.3.11/lib/php/extensions/no-debug-zts-20180731/memcache.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0