RFR: JDK-8206125: [windows] cannot pass relative path to --with-boot-jdk

[Erik Joelsson]

On Windows, the BASIC_FIXUP_PATH macro in configure does not actually 
convert relative paths to absolute like the description claims. This 
patch takes the implementation already present for Unix and applies it 
to all the different Windows environment specific implementations. I 
have verified that it's now possible to use relative paths as well as ~ 
based paths in both Cygwin and WSL for the --with-jtreg parameter, and 
relative paths for --with-boot-jdk.

Bug: https://bugs.openjdk.java.net/browse/JDK-8206125

Webrev: http://cr.openjdk.java.net/~erikj/8206125/webrev.01/

/Erik