Broken zlib detection on OpenSUSE

[stefan6419846]

I tried to build the package on OpenSUSE 15.4, but for some reasons I got told:

checking for library containing gzgets... no
configure: error: HTMLDOC requires zlib.

After changing the offending line of configure.ac from

htmldoc/configure.ac

Line 236 in 055acba

AC_SEARCH_LIBS([gzgets], [z], [

to

AS_IF([$PKGCONFIG --exists zlib], [

and regenerating the configure script, everything worked fine afterwards.

[michaelrsweet]

Not every OS uses pkg-config, so we need to use the AC_SEARCH_LIBS if there is no zlib package file.

[michaelrsweet]

[master 6d7d843] Use pkg-config for initial zlib check (Issue #519)