[Bug libstdc++/84773] New: [7/8 Regression] Cross-compilers do not use aligned_alloc or _aligned_malloc for aligned-new

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84773

            Bug ID: 84773
           Summary: [7/8 Regression] Cross-compilers do not use
                    aligned_alloc or _aligned_malloc for aligned-new
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Native compilers check for:

  AC_CHECK_FUNCS(aligned_alloc posix_memalign memalign _aligned_malloc)

but cross-compilers don't. This means that a cross-compiler for mingw32 will
use the internal definition of aligned_alloc added for PR libstdc++/79190 but a
native ming32 compiler will use _aligned_malloc instead. That means objects
compiled with the cross-compiler are not compatible with objects compiled with
the native one.

On FreeBSD the same problem prevents bootstrapping a cross-compiler:
https://gcc.gnu.org/ml/gcc-help/2017-11/msg00038.html
Which can be solved by making the cross-compiler check for the same functions
as the native one checks for:
https://gcc.gnu.org/ml/gcc-help/2018-02/msg00095.html