configure.ac: Add libelf to host_libs.

configure.ac: Add libelf to host_libs.

* configure.ac: Add libelf to host_libs.  Enable in-tree configury
of ppl and cloog.  Fix in-tree configury of libelf, skip tests.
Fix portability of test of C++ as bootstrap language.  Add
ppl/src/ppl-config.o to the bootstrap compare exclusion list.
* configure: Rebuild.
* Makefile.def: Drop host and target settings from gmp, mpfr, ppl,
and cloog.  Fix in-tree ppl configuration.  Introduce libelf
in-tree building.
* Makefile.tpl (POSTSTAGE1_CXX_EXPORT): New.
(POSTSTAGE1_HOST_EXPORTS): Use it.
(STAGE[+id+]_CXXFLAGS): New.
(BASE_FLAGS_TO_PASS): Pass it down.
(configure-stage[+id+]-[+prefix+][+module+]): Use it.  Add
extra_exports.
(all-stage[+id+]-[+prefix+][+module+]): Likewise.
(configure-[+prefix+][+module+], all-[+prefix+][+module+]): Add
extra_exports.
* Makefile.in: Rebuild.

From-SVN: r154211