hg: build-infra/jdk8: Clean up old LEGACY_OPENJDK_TARGET_CPU3:

[magnus.ihse.bursie at oracle.com]

Changeset: ee34c23829a7
Author:    ihse
Date:      2012-08-16 11:24 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk8/rev/ee34c23829a7

Clean up old LEGACY_OPENJDK_TARGET_CPU3:
* Rename it to OPENJDK_TARGET_CPU_ISADIR
* Remove old use of ISA_DIR. (Kept for hotspot, though)
* Remove the BUILD-version (only TARGET needed)
* Put logic in one place for setting it up, in platform.m4
* Document it more clearly.

! common/autoconf/libraries.m4
! common/autoconf/platform.m4
! common/autoconf/spec.gmk.in
! common/autoconf/spec.sh.in