RFR: JDK-8158535: Configure script uses basic tools directly in many places

[Erik Joelsson]

In the configure script we check for the presence of several basic 
tools, like grep, sed, echo etc, and assign variables for them. In the 
makefiles we are very diligent with always using the tools through these 
variables to make sure we have a well functioning version of the tool at 
hand. In many places in the configure script, we have been sloppy with 
this.

I recently stumbled over this because we change the PATH variable in 
parts of the script (typically when looking for the toolchain) which can 
then potentially change which instance of the tool that is being run 
unless the resolved variables are used. This patch fixes all the 
instances that I could find.

Bug: https://bugs.openjdk.java.net/browse/JDK-8158535
Webrev: http://cr.openjdk.java.net/~erikj/8158535/webrev.top.01/

/Erik