[Bug libffi/65726] New: [5.0 regression] libffi fails to build (with clang) when not bootstrapping: configure: error: C++ preprocessor "/lib/cpp" fails sanity check

[gerald at pfeifer dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65726

            Bug ID: 65726
           Summary: [5.0 regression] libffi fails to build (with clang)
                    when not bootstrapping: configure: error: C++
                    preprocessor "/lib/cpp" fails sanity check
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libffi
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gerald at pfeifer dot com
                CC: rth at gcc dot gnu.org
              Host: i386-unknown-freebsd10.1

Created attachment 35283
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35283&action=edit
builddir/i386-portbld-freebsd10.1/libffi/config.log

This seems to be a regression with the new libffi changes past GCC 4.9.

When building on recent versions of FreeBSD where clang is the system
compiler, without a bootstrap this is what we get:

configure: error: in `/scratch2/tmp/gerald/gcc5-w
ork/build/i386-portbld-freebsd10.1/libffi':
configure: error: C++ preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details.


Why is it trying to use /lib/cpp which does not even exist?