Add configure option(s) to allow for full debug symbols in native files as well as java class files

This bug has two angles:
- full debug symbols for native files (such as hotspot and JDK natives). Think gcc's -g option.
- full debug symbols for Java class files. Think javac's -g option.

A solution to this should be consistent across hotspot and JDK.

Both issues are major pain points and - interestingly - once fixed seem to surface again after some time. It seems time to fix this once and for all (including regression tests).

Background:
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Many Linux distributions have the requirement to build native libraries with full debug symbols with them *not* being stripped at the end of the build. That is, independent of the "type" of the build, which is oddly named --with-debug-level (that takes values "fastdebug", "slowdebug" or "release"). For example we build OpenJDK in Fedora with --with-debug-level=release but want full debug symbols in the resulting binaries. Debug symbols get stripped after the binaries got built.

Similarly, Linux distributions build packages from source and it is useful to have full debug symbols for Java class files provided by the JDK available. There should be a configure option which allows this. There used to be a DEBUG_CLASSFILES make variable which now seems largely unused.

References:
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Related threads and bugs for the native debug symbols issues:
http://mail.openjdk.java.net/pipermail/build-dev/2013-April/008543.html
http://mail.openjdk.java.net/pipermail/build-dev/2014-March/012047.html

Related threads and bugs for the Java class file debug info issues:
http://mail.openjdk.java.net/pipermail/build-dev/2012-December/007456.html
http://mail.openjdk.java.net/pipermail/build-dev/2014-October/013397.html
https://bugs.openjdk.java.net/browse/JDK-8046309

Related to both?
https://bugs.openjdk.java.net/browse/JDK-8036003
https://bugs.openjdk.java.net/issues/?jql=labels%20%3D%20FDS (FDS labelled bugs)