Automake issues on pngnq

[Andreas Tille <andreas@an3as.eu>]

Hi,

I tried to adopt pngnq from QA and pushed it to Salsa[1].
Unfortunately the new upstream version has some automake issues.

Strangely enough one issue in configure script occures only in
salsa-ci[2] but not in my local pbuilder.  There I get another
issue in a later stage of the build process:

gcc `libpng-config --I_opts` -Wall --pedantic -std=gnu99 -g -O2 -ffile-prefix-map=/build/pngnq-1.1=. -fstack-protector-strong -Wformat -Werror=format-security `libpng-config --ldflags` -lz -lm -Wl,-z,relro -Wl,-z,now  -o pngcomp pngcomp.o rwpng.o colorspace.o  -lm -lz 
/usr/bin/ld: rwpng.o: in function `rwpng_error_handler':
./src/rwpng.c:563: undefined reference to `png_get_error_ptr'
/usr/bin/ld: rwpng.o: in function `rwpng_version_info':
./src/rwpng.c:48: undefined reference to `png_get_header_ver'
/usr/bin/ld: rwpng.o: in function `rwpng_read_image':
./src/rwpng.c:82: undefined reference to `png_sig_cmp'
/usr/bin/ld: ./src/rwpng.c:88: undefined reference to `png_create_read_struct'
...


The latter can be fixed by appending `libpng-config --ldflags` in the
end of the command line.  For whatever reason automake puts LDFLAGS
before "-o pngcomp" instead of after and the last options are obtained
from the LIBS variable.  I have no idea how to tweak this sequence.

Kind regards

     Andreas.


[1] https://salsa.debian.org/debian-phototools-team/pngnq/
[2] https://salsa.debian.org/debian-phototools-team/pngnq/-/jobs/2538883

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