[Bug bootstrap/87030] GCC fails to build with Xcode 10, attempting an impossible multilib build

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87030

--- Comment #9 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Sat, 8 Sep 2018, iains at gcc dot gnu.org wrote:

> 2. Actually, you get the same failure on GNU-Linux if you try to configure
> defaults on (for example) an x86_64 system without 32bit libs installed (one
> has to add --disable-multilib there, or install 32b libs), so automation is not
> the default on Linux.

The toplevel configure.ac code

# Special user-friendly check for native x86_64-linux build, if
# multilib is not explicitly enabled.
case "$target:$have_compiler:$host:$target:$enable_multilib" in
  x86_64-*linux*:yes:$build:$build:)
    # Make sure we have a development environment that handles 32-bit
[...]

is meant to give a more helpful error in that case:

AC_MSG_ERROR([I suspect your system does not have 32-bit development 
libraries (libc and headers). If you have them, rerun configure with 
--enable-multilib. If you do not have them, and want to build a 
64-bit-only compiler, rerun configure with --disable-multilib.])