present but cannot be compiled (Was: dlfcn.h: accepted by the compiler, rejected by the preprocessor!)

[Akim Demaille]

Please, report this to the package maintainers, as it's a configure.ac
problem.  The Autoconf 2.57 doc says:

      Previous versions of Autoconf merely checked whether the header was
   accepted by the preprocessor.  This was changed because the old test was
   inappropriate for typical uses.  Headers are typically used to compile,
   not merely to preprocess, and the old behavior sometimes accepted
   headers that clashed at compile-time.  If you need to check whether a
   header is preprocessable, you can use `AC_PREPROC_IFELSE' (*note
   Running the Preprocessor::).
   
      This scheme, which improves the robustness of the test, also requires
   that you make sure that headers that must be included before the
   HEADER-FILE be part of the INCLUDES, (*note Default Includes::).  If
   looking for `bar.h', which requires that `foo.h' be included before if
   it exists, we suggest the following scheme:
   
   
   AC_CHECK_HEADERS([foo.h])
   AC_CHECK_HEADERS([bar.h], [], [],
   [#if HAVE_FOO_H
   # include <foo.h>
   # endif
   ])

Thanks!

| I guess you already know this.. but autoconf told me to send this mail
| and I would never object with him 0=)
| 
| configure: WARNING: dlfcn.h: accepted by the compiler, rejected by the
| preprocessor!
| configure: WARNING: dlfcn.h: proceeding with the preprocessor's result
| configure: WARNING:     ## ------------------------------------ ##
| configure: WARNING:     ## Report this to address@hidden ##
| configure: WARNING:     ## ------------------------------------ ##
| 
| $ uname -a
| CYGWIN_NT-5.1 CYBERONE 1.3.17(0.67/3/2) 2002-11-27 18:54 i686 unknown
| unknown Cygwin
| $ autoconf --version
| autoconf (GNU Autoconf) 2.57
| $ gcc -v
| Reading specs from /usr/lib/gcc-lib/i686-pc-cygwin/3.2/specs
| Configured with: /netrel/src/gcc-3.2-3/configure
| --enable-languages=c,c++,f77,java --enable-libgcj
| --enable-threads=posix --with-system-zlib --enable-nls
| --without-included-gettext --enable-interpreter
| --disable-sjlj-exceptions --disable-version-specific-runtime-libs
| --enable-shared --build=i686-pc-linux --host=i686-pc-cygwin
| --target=i686-pc-cygwin --enable-haifa --prefix=/usr
| --exec-prefix=/usr --sysconfdir=/etc --libdir=/usr/lib
| --includedir=/nonexistent/include --libexecdir=/usr/sbin
| Thread model: posix
| gcc version 3.2 20020927 (prerelease)
| $ ccache -V
| ccache version 1.9
| Copyright Andrew Tridgell 2002
| Released under the GNU GPL v2 or later