7132779: build-infra merge: Enable ccache to work for most developer builds. Summary: When a build number is not specified, the JRE_RELEASE_VERSION define contains a date and timestamp. Thus ccache cannot cache the object files for longer than a minute since the define is passed to the compilation of all source files. This change passes JRE_RELEASE_VERSION only to vm_version.cpp and adds a function jre_release_version() to Abstract_VM_Version. This allows all other source files to be ccached. Reviewed-by: ohair, rottenha Contributed-by: fredrik.ohrstrom@oracle.com

README:
  This file should be located at the top of the hotspot Mercurial repository.

  See http://openjdk.java.net/ for more information about the OpenJDK.

  See ../README-builds.html for complete details on build machine requirements.

Simple Build Instructions:

    cd make && gnumake
     
  The files that will be imported into the jdk build will be in the "build"
  directory.