configure.in (LIBSUPCXX_PICFLAGS): Set it to -prefer-pic or -prefer-non-pic depending on whether libtool has...

* configure.in (LIBSUPCXX_PICFLAGS): Set it to -prefer-pic or
-prefer-non-pic depending on whether libtool has shared libraries
enabled or disabled.
* libsupc++/Makefile.am (LIBSUPCXX_CXXFLAGS): Set to
$(LIBSUPCXX_PICFLAGS).
* configure, */Makefile.in: Rebuilt.

From-SVN: r41806