[v3] weak instantiations for AIX

[David Edelsohn]

	Two of the remaining failures are locale problems.  Only the
27_io/basic_istream/extractors_arithmetic/char/12.cc failure seems to be
fundamental.


terminate called after throwing an instance of 'std::runtime_error'
  what():  attempt to create locale from unhandled name in generic implementation; see http://gcc.gnu.org/ml/libstdc++/2003-02/msg00345.html
FAIL: 22_locale/locale/cons/3.cc execution test

Assertion failed: __EX, file  /gcc/dje/src/libstdc++-v3/testsuite/27_io/basic_istream/extractors_arithmetic/char/12.cc, line 74
FAIL: 27_io/basic_istream/extractors_arithmetic/char/12.cc execution test

terminate called after throwing an instance of 'std::runtime_error'
  what():  attempt to create locale from unhandled name in generic implementation; see http://gcc.gnu.org/ml/libstdc++/2003-02/msg00345.html
FAIL: 27_io/ios_base/state/1.cc execution test


Thanks, David