configure: WARNING: png.h: accepted by the compiler, rejected by the preprocessor!

[Klaus Fehlker]

Hello,
i tried to configure CUPS 1.1.23 on HP-UX and it gave me the following error
telling me to report the bug.
Could you please let me know whether this bug is still valid and if not
where i can get information to resolve it?
Thanks,
Klaus Fehlker

Environment:
hostname = parhs003
uname -m = 9000/800
uname -r = B.11.11
uname -s = HP-UX
uname -v = U
CCFLAGS='-I/usr/local/include -I/opt/libpng/include'
CFLAGS='-I/usr/local/include -I/opt/libpng/include'
CXXFLAGS='-I/usr/local/include -I/opt/libpng/include'
DSOFLAGS='-L/usr/local/lib -L/opt/libpng/lib'
LDFLAGS='-L/usr/local/lib -L/opt/libpng/lib'

Configure output:
checking png.h usability... yes
checking png.h presence... no
configure: WARNING: png.h: accepted by the compiler, rejected by the
preprocessor!
configure: WARNING: png.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
checking for png.h... no


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