[RFR] [8u-JFR] 8238076: Fix OpenJDK 7 Bootstrap Broken by JFR Backport

[Andrew John Hughes]

Webrev: https://cr.openjdk.java.net/~andrew/openjdk8/8238076/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8238076

The initial backport of JFR in JDK-8223147 introduced a new bootstrap
tool, src/share/vm/jfr/GenerateJfrFiles.java, within the HotSpot tree.
Rather than adapting the tool to work with the existing source & target
options used for bootstrap tools, JDK-8223147 bumped them to 8. In doing
so, it broke the ability to build the JDK with the previous version (7).

The lambda constructs & use of StringJoiner in GenerateJfrFiles.java can
be easily replaced with Java 7 compatible usage, thus retaining the
ability to bootstrap the JDK. The BOOT_SOURCE_LANGUAGE_VERSION and
BOOT_TARGET_CLASS_VERSION are moved back down to 7 on *BSD, Linux,
Solaris & Windows.

It seems the values were still at 6 on AIX, so I can only presume the
build hasn't been tested there. I raised those up to 7 for consistency.
I guess we could have gone back to 6, but there is no intention to
support building with OpenJDK 6 anyway.

Ok for JFR tree?

Thanks,
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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