RFR: 8015377: Support using compiler devkits on Linux

[Erik Joelsson]

Official compiler and OS versions for building OracleJDK are being 
evaluated. A wanted feature is to be able to separate compiler version 
from OS version for the linux build, as is already the case for all 
other platforms. This could be achieved by creating portable self 
contained compiler bundles. Support for such devkits already exist in 
the OpenJDK configure scripts, but since it's rarely used, there are a 
couple of issues with it that needs to be fixed.

This patch fixes those issues and also provides makefiles that can be 
used to replicate the devkits being evaluated. More information on how 
to build them can be found in the comments in 
common/makefiles/devkit/Makefile. I don't expect many will try this, but 
the information should be open. These makefiles could be left for later. 
The configure changes are what we need now.

A devkit like this solves several problems:
1. We need to build on an older OS to create binaries compatible with 
both old and new versions of OSes, but we also want to use modern 
compilers not likely to be available on an older OS.
2. For developers it's easier to get a working build environment on a 
new system since most dependencies will be in the devkit. It also makes 
it easier to use the official compiler and libraries for developer builds.
3. Support for cross compilation is included. The x86_64 package 
supports the -m32 flag and will function correctly when the jdk 
configure script is fed with --with-target-bits=32. The i686 package 
contains a full x86_64 cross toolchain.

http://cr.openjdk.java.net/~erikj/8015377/webrev.root.01/

Binary bundles will be made available internally soon.

/Erik