PR libstdc++/51083
* include/ext/type_traits.h (__promote): Only define __type member
for integral and floating point types, to prevent math functions
participating in overload resolution for other types.
(__promote_2, __promote_3, __promote_4): Use __promote in default
template argument values, so deduction only succeeds for integral and
floating point types.
* testsuite/26_numerics/cmath/51083.cc: New.
* testsuite/26_numerics/complex/51083.cc: New.
* testsuite/tr1/8_c_compatibility/cmath/51083.cc: New.
* testsuite/tr1/8_c_compatibility/complex/51083.cc: New.
From-SVN: r181321
