Error checking for dlfcn.h header

[Robin]

Hi,

I get an error running the dlfcn.h header check inside a configure file.
A snippet from the output log is as follows:

        ########################################################################
        ### Initializing libtool                                             ###
        ########################################################################
        checking for a sed that does not truncate output... /bin/sed
        checking for ld used by cc... /usr/bin/ld
        checking if the linker (/usr/bin/ld) is GNU ld... yes
        checking for /usr/bin/ld option to reload object files... -r
        checking for BSD-compatible nm... /usr/bin/nm -B
        checking whether ln -s works... yes
        checking how to recognise dependent libraries... pass_all
        checking dlfcn.h usability... yes
        checking dlfcn.h presence... configure: WARNING: dlfcn.h: accepted by 
the compiler, rejected by the preprocessor!
        configure: WARNING: dlfcn.h: proceeding with the preprocessor's result
        no
        configure: WARNING:     ## ------------------------------------ ##
        configure: WARNING:     ## Report this to address@hidden ##
        configure: WARNING:     ## ------------------------------------ ##
        checking for dlfcn.h... no
        checking how to run the C++ preprocessor... g++ -E

A look at the config.log file reveals that the value for the
preprocessor is not set, which causes the dlfcn.h presence check to
fail. And sure enough, if you run it like this:
        CXXCPP="g++ -E" ./configure
the above test completes successfully.

What gives? Is this really a bug in autoconf?
I am not entirely sure if this is an autoconf bug, since it could be in
libtool -- the above lines I think are related to the AC_PROG_LIBTOOL
target in my configure.in. If it has nothing to do with autoconf as
such, please let me know where to complain :-)

It seems to me that the check for dlfcn.h, which relies on the C++
preprocessor, should be executed after the check for said preprocessor.

Regards,
Robin