RFR: 8193189: Allow --boot-jdk to accept a .tar.gz compressed JDK image

[Erik Helin]

Hi all,

this small patch allows the --boot-jdk flag to configure to accept a 
gzip compressed JDK image. For example:

  $ wget 
http://download.java.net/java/GA/jdk9/9.0.1/binaries/openjdk-9.0.1_linux-x64_bin.tar.gz
  $ bash configure --with-boot-jdk=openjdk-9.0.1_linux-x64_bin.tar.gz

The compressed image will be extracted into 
build/<profile-name>/configure-support/boot-jdk.

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8193189

Patch:
http://cr.openjdk.java.net/~ehelin/8193189/00/

Testing:
- configure and make locally on Linux x86-64

Thanks,
Erik