RFR: 8323675: Race in jdk.javadoc-gendata

[Magnus Ihse Bursie]

In [JDK-8318913](https://bugs.openjdk.org/browse/JDK-8318913), the symbolgenerator started to look at current sources as well. This means that the gensrc stage needs to be completed before this is run. A dependency was added for jdk.compiler-gendata, but unfortunately the same tool is run also in jdk.javadoc-gendata, where no such safeguard was created.

The result is that the build can fail intermittently with:

.../module-info.java:77: error: module not found on module source path
module java.base {
^
error: cannot access module-info
  cannot resolve modules
Exception in thread "main" java.lang.AssertionError
at jdk.compiler.interim/com.sun.tools.javac.util.Assert.error(Assert.java:155)
at jdk.compiler.interim/com.sun.tools.javac.util.Assert.checkNonNull(Assert.java:62)
at jdk.compiler.interim/com.sun.tools.javac.comp.Modules.allModules(Modules.java:1225)
at jdk.compiler.interim/com.sun.tools.javac.comp.Modules.getObservableModule(Modules.java:1450)
at jdk.compiler.interim/com.sun.tools.javac.model.JavacElements.getModuleElement(JavacElements.java:144)
at jdk.compiler.interim/com.sun.tools.javac.model.JavacElements.getModuleElement(JavacElements.java:89)
at build.tools.symbolgenerator.JavadocElementList.main(JavadocElementList.java:98)
Compiling up to 2 files for BUILD_BREAKITERATOR_BASE
Compiling up to 2 files for BUILD_BREAKITERATOR_LD
make[3]: *** [.../_element_lists.marker] Error 1
Gendata.gmk:74: recipe for target '.../_element_lists.marker' failed

-------------

Commit messages:
 - 8323675: Race in jdk.javadoc-gendata

Changes: https://git.openjdk.org/jdk/pull/17402/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17402&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323675
  Stats: 7 lines in 1 file changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/17402.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17402/head:pull/17402

PR: https://git.openjdk.org/jdk/pull/17402