Remove Harmony and related code from OpenJ9 builds

[pdbain-ibm]

Harmony code is required for certain legacy builds, but not Java 9 or OpenJ9.
Request a configuration parameter, e.g. INCLUDE_HARMONY, which is false by default,
in the cmake build system.
@pshipton FYI
@dnakamura will our cmake build system handle different configurations depending on the Java spec version?

[pdbain-ibm]

Prototype: https://github.com/pdbain-ibm/openj9/tree/remove_harmony
This uses the JAVA_SPEC_VERSION compiler command line setting.

[pdbain-ibm]

@DanHeidinga FYI.
Notes so far:

1. IBM Java 8 uses the Harmony JDWP and hence the Harmony port library shim.
   This is about 47 KB on Linux x86.

2. The IBM Java 9 VM should support Java 8, so should load the Harmony shim when running in Java 8.

3. The Java version is checked in jvm.c:JNI_CreateJavaVM(), but does so ~100 lines after calling preloadLibraries() (which loads J9_HARMONY_PORT_LIBRARY_SHIM_DLL_NAME).

4. JVM initialization adds an argument to the VM arguments with a pointer to the Harmony port library.

5. runtime/vm/vmifunc.c sets up the Harmony VMI functions. In doing so, it scans the VM arguments for the setting from 4).

6. This branch: https://github.com/pdbain-ibm/openj9/tree/disable_harmony has code to disable 4) and 5). The change is fairly simple since the Java version is known. Avoiding loading the shim is a bigger job because the version isn't known at the time.

7. The OpenJ9 Java 8 & 9 VMs do not need the Harmony code. There is currently no build flag to distinguish IBM from OpenJ9 builds, though.

[pdbain-ibm]

See also #621

[pdbain-ibm]

Comment from same:
dnakamura 14 days ago • edited Contributor
Alternatively the -D/-U options I added to UMA could come in handy here. It lets you override buildspec flag settings on the command line. This is done by passing -D or -U to set/unset the option respectively. ie -D opt_harmony
Edit: See #78 for details

[pdbain-ibm]

Per discussion with @pshipton, removing Harmony also allows us to remove some port library socket code.

[pdbain-ibm]

Picking this up again. The entire socket code is still required for Harmony in the proprietary builds
but only a subset is required for OpenJ9.
Two approaches to removing the socket code:

1. split the socket library and move the functions needed by Harmony to an internal repo.
2. ifdef out the functions required by Harmony.

@DanHeidinga FYI.