RFR: 8255801: Race when building ct.sym build tools

[Magnus Ihse Bursie]

There is a race when compiling build.tools.symbolgenerator.CreateSymbols:

[2020-11-03T07:21:12,118Z] Error: LinkageError occurred while loading main class build.tools.symbolgenerator.CreateSymbols
[2020-11-03T07:21:12,119Z] java.lang.ClassFormatError: Truncated class file
[2020-11-03T07:21:12,125Z] Gendata.gmk:69: recipe for target '/.../build/macosx-x64-open/support/javadoc-symbols/symbols' failed
[2020-11-03T07:21:12,125Z] make[3]: *** [/.../build/macosx-x64-open/support/javadoc-symbols/symbols] Error 1
[2020-11-03T07:21:12,127Z] make/Main.gmk:148: recipe for target 'jdk.javadoc-gendata' failed
[2020-11-03T07:21:12,127Z] make[2]: *** [jdk.javadoc-gendata] Error 2
[2020-11-03T07:21:12,127Z] make[2]: *** Waiting for unfinished jobs....

This was caused by https://bugs.openjdk.java.net/browse/JDK-8216497, which started compiling the same buildtool twic, in different, independent makefiles, to the same output directory.

The long term correct solution is to fix https://bugs.openjdk.java.net/browse/JDK-8241463.

For now, I opted to just make sure the output is placed in separate directories to avoid the race. We will still compile the build tool twice; it's annoying but not a major performance problem.

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Commit messages:
 - 8255801: Race when building ct.sym build tools

Changes: https://git.openjdk.java.net/jdk/pull/1037/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1037&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255801
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1037.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1037/head:pull/1037

PR: https://git.openjdk.java.net/jdk/pull/1037