[Bug other/95316] New: [10 Regression] binary built with -fopenacc fails to run when not all offload compilers are installed that were configured

["doko at debian dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95316

            Bug ID: 95316
           Summary: [10 Regression] binary built with -fopenacc fails to
                    run when not all offload compilers are installed that
                    were configured
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: doko at debian dot org
  Target Milestone: ---

This is usage regression; in gcc-9 building with

  gcc-9 -o mandel-accel mandel.c -Wall -O2 -fopenacc

and running the mandel-accel binary works, if the nvptx offload compiler is
installed.

Building that with gcc-10 leads to:

$ gcc-10 -o mandel-accel mandel.c -Wall -O3 -fopenacc
lto-wrapper: fatal error: could not find accel/amdgcn-amdhsa/mkoffload in
/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/
(consider using ‘-B’)
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed

because gcc-10 was configured with more than one offload target.  Installing
all configured offload compilers works around it, or building for the offload
targets explicitly (-foffload=nvptx-none).

Expected behavior:  Just print a warning when an offload compiler for a target
cannot be found.

Note: the packaged compilers for Debian/Ubuntu are gcc-10, gcc-10-offload-nvptx
and gcc-10-offload-amdgcn.

See https://launchpad.net/bugs/1878760