[Issue 20355] New: undefined identifier U in core.atomic

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20355

          Issue ID: 20355
           Summary: undefined identifier U in core.atomic
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: blocker
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: bitworld at qq.com

The full log:

:~/dlang/hunt/examples/UnitTest/ > dub build --compiler=dmd -a=x86_64 -b=debug 
Performing "debug" build using dmd for x86_64.
hunt 1.4.0+commit.9.gb640ab1: building configuration "library"...
/home/dmd2/linux/bin64/../../src/druntime/import/core/atomic.d(246,23): Error:
undefined identifier U
../../source/hunt/concurrency/atomic/AtomicHelper.d(51,41): Error: template
instance core.atomic.atomicExchange!(cast(MemoryOrder)5, IForkJoinTask,
shared(IForkJoinTask)) error instantiating
../../source/hunt/concurrency/ForkJoinPool.d(3358,43):        instantiated from
here: getAndSet!(IForkJoinTask, IForkJoinTask)

See also:
https://travis-ci.org/huntlabs/hunt/jobs/607449502

https://github.com/huntlabs/hunt/blob/master/source/hunt/concurrency/ForkJoinPool.d#L1383
https://github.com/huntlabs/hunt/blob/master/source/hunt/concurrency/atomic/AtomicHelper.d#L27

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