GitLab

While it affects all branches, it is intended to fix the following
flang build failure on llvm.org/main:

```
/auto/ciscratch/builds/o5chMQGp/0/llvm-doe/llvm-project/flang/runtime/sum.cpp:51:17: error: __float128 and long double cannot be used in the same expression
   51 |     auto next{x + correction_};
      |               ~~^~~~~~~~~~~~~
/auto/ciscratch/builds/o5chMQGp/0/llvm-doe/llvm-project/flang/runtime/sum.cpp:51:10: error: unable to deduce ‘auto’ from ‘<expression error>’
   51 |     auto next{x + correction_};
      |
```

Upstream's 2fb131668fff just fixed the bug.

It's too noisy.

`-DCLANG_DEFAULT_LINKER=lld` didn't help.  Try prepending the build's
bin directory to PATH.

libomptarget's amdgpu tests have been failing with errors like the
following for about a week:

```
/auto/ciscratch/builds/xjSVwmna/0/llvm-doe/llvm-project/build/./bin/clang-linker-wrapper: error: Unable to find 'lld' in path
```

The following builds use `-DCLANG_DEFAULT_LINKER=lld` and don't have
that failure, so try that:

  <https://lab.llvm.org/buildbot/#/builders/193/builds/10825/steps/4/logs/stdio>

Due to recent merges from upstream.

llvm.org/main f054d291f22a reverted the fix in d6623d72461b, so
check-all once again does not include check-openmp.  To work around
that, run check-openmp alongside check-all.

llvm.org/main d6623d72461b just fixed the recent bug that check-all
omits check-openmp.  This CI config's 0c1733ea worked around that bug
by running check-openmp separately.  Revert the latter commit so we
don't run check-openmp twice now.  Moreover, check-all now runs all
test suites in one lit invocation instead of two, so update comments
about the use of --ignore-fail.

It's not clear what has caused the affected tests to pass so often
now, but they do seem to pass more often than fail now.

GCC 11.1.0 has been built with "go" support.

GCC 11.1.0 now has "go" support.

`CLANG_ACC_TEST_EXE_` cmake variables are no longer needed.

AMD GPUs are supported, so test on explorer.

... so it doesn't affect explorer and kold00, which were already
working.