[Bug libstdc++/58393] New: Please relax feature check for std::to_string and std::sto* for uClibc

["nicolas.cavallari at lri dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58393

            Bug ID: 58393
           Summary: Please relax feature check for std::to_string and
                    std::sto* for uClibc
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nicolas.cavallari at lri dot fr

Created attachment 30800
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30800&action=edit
Relax constraints on std::to_w?string and std:sto*

The GCC build system's feature check that must be passed to enable support for
std::to_w?string and std::sto.* asks for the underlying C library to support a
large set of C99 functions, including C99 real and complex math.

uClibc does not implement complex math function and the C99 real math functions
are optional.

The implementation of std::to_w?string and std::sto.* do not use complex math
functions and probably never will, so it is a bit sad that a libstdc++ built
against uClibc does not provide std::to_w?string and std::sto.*

The feature check should be relaxed to only requires the functions that are
actually used to implement std::to_w?string and std::sto.*

The attached patch is an example of how it could be done.