Undefined reference to COMB with NOTHREADS

[Nathan Moinvaziri]

We get this new error in our CI when NOTHREADS is defined with pigz 2.7 cb8a432:

[ 95%] Building C object CMakeFiles/pigz.dir/_deps/pigz-src/pigz.c.o
/home/runner/work/zlib-ng/zlib-ng/test/pigz/_deps/pigz-src/pigz.c:3598:20: warning: implicit declaration of function 'COMB' is invalid in C99 [-Wimplicit-function-declaration]
[ 97%] Building C object CMakeFiles/pigz.dir/_deps/pigz-src/try.c.o
[100%] Linking C executable pigz
/usr/bin/ld: CMakeFiles/pigz.dir/_deps/pigz-src/pigz.c.o: in function `infchk':
pigz.c:(.text+0xdbcb): undefined reference to `COMB'

https://github.com/zlib-ng/zlib-ng/runs/4828890476?check_suite_focus=true
Clang 11.0.0, Ubuntu 20

[Mark Adler]

Whoops. Thanks for testing NOTHREAD. Fixed in this commit: 67fd6e4