[Bug bootstrap/49502] Unable to build gcc with gmp/mpc/mpfr in its tree and flag "--enable-cxx"

["franck.z.bugzilla at orange dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49502

--- Comment #4 from Franck Z <franck.z.bugzilla at orange dot fr> 2011-06-23 18:45:33 UTC ---
(In reply to comment #3)

gotcha!

It's in PPL's configure script.
When checking for the correct version of gmp, the line:

#include <gmpxx.h>

is used several times and this is what choked my building session.

Later the script analyses the error and advises --enable-cxx (it's around the
middle of the script):

if test x"$have_gmp" = xno
then
  as_fn_error "Cannot find GMP version 4.1.3 or higher.
GMP is the GNU Multi-Precision library:
see http://www.swox.com/gmp/ for more information.
When compiling the GMP library, do not forget to enable the C++ interface:
add --enable-cxx to the configuration options." "$LINENO" 5
else
  if test x"$have_gmpxx" = xno
  then
    as_fn_error "GMP compiled without enabling the C++ interface.
GMP is the GNU Multi-Precision library:
see http://www.swox.com/gmp/ for more information.
When compiling the GMP library, do not forget to enable the C++ interface:
add --enable-cxx to the configuration options." "$LINENO" 5
  fi
fi

Now, apparently, as I separate the output of the compilation in a special
"objdir" directory, gmpxx.h can't be found with the paths in objdir/gmp/
because only gmp.h and mp.h are placed there. gmpxx.h is copied later from the
source directory by gmp with the "make install" command.

I should write also that this script didn't mention the absence of gmpxx.h in
objdir when a system version of gmp was already installed, for instance in
/usr/local/lib & /usr/local/include. Ominous, no?

That being said. I'll keep away from PPL and Cloog as you suggests... ^o^ ...
until I know more my way in gcc.

(--enable-cxx is indeed referenced in the pdf manual of gmp, p.6)