Formal request for review: 7025066 Build system changes to support SE Embedded integration

[David Holmes]

webrev: http://cr.openjdk.java.net/~dholmes/7025066/webrev/

This places the SE-Embedded specific targets and definitions into 
Release-embedded.gmk and Defs-embedded.gmk respectively. These files are 
unconditionally included but then guarded with ifdef JAVASE_EMBEDDED 
internally. This avoids the need for JAVASE_EMBEDDED to appear in the 
main build files.

Additional changes:

- some control over whether certain jars are compressed or not
- make ALSA version check conditional of having REQUIRED_ALSA_VERSION 
defined
- control use of USE_MMAP flag for zip

The final chunk here will be AWT related updates.

Then an update to the builds readme in the top-level repo.

Thanks,
David