Internal Compiler Error when trying to compile openpgp npm module

```
curl -O https://unpkg.com/openpgp@4.0.0/dist/openpgp.js
npx google-closure-compiler --js=openpgp.js --js_output_file=out.js
```

yields a whole lot of warnings and errors and ultimately fails with

```
java.lang.RuntimeException: INTERNAL COMPILER ERROR.
Please report this problem.

INTERNAL COMPILER ERROR.
Please report this problem.

null
Node(FUNCTION ): openpgp.js:38405:70
SymmetricallyEncrypted.prototype.encrypt = async function (algo, key) {
Parent(CALL): openpgp.js:38405:70
SymmetricallyEncrypted.prototype.encrypt = async function (algo, key) {

at java.lang.Throwable.(Throwable.java:250)
at java.lang.Exception.(Exception.java:54)
at java.lang.RuntimeException.(RuntimeException.java:51)
at java.lang.IllegalStateException.(IllegalStateException.java:44)
at com.google.common.base.Preconditions.checkState(Preconditions.java:491)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler$YieldFinder.shouldTraverse(Es6RewriteGenerators.java:1143)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:830)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverse(NodeTraversal.java:331)
at com.google.javascript.jscomp.NodeTraversal.traverse(NodeTraversal.java:341)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.findYield(Es6RewriteGenerators.java:1128)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.transpileYields(Es6RewriteGenerators.java:698)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.transpileExpressionResult(Es6RewriteGenerators.java:573)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.transpileStatement(Es6RewriteGenerators.java:474)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.transpileStatement(Es6RewriteGenerators.java:442)
at com.google.javascript.jscomp.Es6RewriteGenerators$SingleGeneratorFunctionTranspiler.transpile(Es6RewriteGenerators.java:422)
at com.google.javascript.jscomp.Es6RewriteGenerators$GeneratorFunctionsTranspiler.visit(Es6RewriteGenerators.java:220)
at com.google.javascript.jscomp.NodeTraversal.handleFunction(NodeTraversal.java:811)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:825)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBlockScope(NodeTraversal.java:974)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:841)
at com.google.javascript.jscomp.NodeTraversal.traverseFunction(NodeTraversal.java:886)
at com.google.javascript.jscomp.NodeTraversal.handleFunction(NodeTraversal.java:809)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:825)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBlockScope(NodeTraversal.java:974)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:841)
at com.google.javascript.jscomp.NodeTraversal.traverseFunction(NodeTraversal.java:886)
at com.google.javascript.jscomp.NodeTraversal.handleFunction(NodeTraversal.java:809)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:825)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBlockScope(NodeTraversal.java:974)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:841)
at com.google.javascript.jscomp.NodeTraversal.traverseFunction(NodeTraversal.java:886)
at com.google.javascript.jscomp.NodeTraversal.handleFunction(NodeTraversal.java:809)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:825)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:843)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:959)
at com.google.javascript.jscomp.NodeTraversal.handleScript(NodeTraversal.java:797)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:822)
at com.google.javascript.jscomp.NodeTraversal.traverse(NodeTraversal.java:331)
at com.google.javascript.jscomp.NodeTraversal.traverse(NodeTraversal.java:341)
at com.google.javascript.jscomp.TranspilationPasses.processTranspile(TranspilationPasses.java:540)
at com.google.javascript.jscomp.Es6RewriteGenerators.process(Es6RewriteGenerators.java:120)
at com.google.javascript.jscomp.PhaseOptimizer$NamedPass.process(PhaseOptimizer.java:307)
at com.google.javascript.jscomp.PhaseOptimizer.process(PhaseOptimizer.java:230)
at com.google.javascript.jscomp.Compiler.check(Compiler.java:1056)
at com.google.javascript.jscomp.Compiler.performChecksAndTranspilation(Compiler.java:849)
at com.google.javascript.jscomp.Compiler.access$000(Compiler.java:109)
at com.google.javascript.jscomp.Compiler$2.call(Compiler.java:783)
at com.google.javascript.jscomp.Compiler$2.call(Compiler.java:780)
at com.google.javascript.jscomp.CompilerExecutor$2.call(CompilerExecutor.java:102)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
at com.oracle.svm.core.posix.thread.PosixJavaThreads.pthreadStartRoutine(PosixJavaThreads.java:238)
Caused by: java.lang.RuntimeException: INTERNAL COMPILER ERROR.
Please report this problem.

null
... 84 more
Caused by: java.lang.IllegalStateException
... 84 more
```