[Bug libstdc++/78110] freestanding libstdc++ fails to compile

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78110

--- Comment #1 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
oh, I am using eCos and that is based on newlib but on a very very old one.
I don't know what happens when I dont use --with-newlib, but I can try...

configure.ac has this:
  # First, test for "known" system libraries.  We may be using newlib even
  # on a hosted environment.
  if test "x${with_newlib}" = "xyes"; then
    os_include_dir="os/newlib"
    AC_DEFINE(HAVE_HYPOT)

...

    AC_DEFINE(HAVE_ICONV)
    AC_DEFINE(HAVE_MEMALIGN)

why are these not compile-time checks, to see if the headers are available?