[15] RFR: JDK-8249255: Build fails if source code in cygwin home dir

[Tim Bell]

Erik:

 > The fix is to make sure WORKSPACE_ROOT in basics.m4 only gets values
 > that have been fixed using UTIL_FIXUP_PATH.

Looks good.

Tim

> This is a fix for the problem reported by Ty in this thread: 
> https://mail.openjdk.java.net/pipermail/build-dev/2020-July/027917.html
> 
> The problem is the --disable-absolute-paths-in-output option, which is 
> default set to disable on release builds. When not allowing absolute 
> paths, we rewrite absolute paths to relative in several types of build 
> command lines. This rewrite relies on the WORKSPACE_ROOT variable to be 
> fully resolved. Currently, if the workspace is located inside the cygwin 
> root dir, the WORKSPACE_ROOT variable will have a path looking like 
> "/home/user/jdk" while all other paths that we resolve files from will 
> look like "/cygdrive/c/cygwin64/home/user/jdk". This causes the rewrite 
> to fail and results in build errors like this:
> 
> c1xx: fatal error C1083: Cannot open source file: 
> '../../../..c:/cygwin64/home/young/jdk-master/jdk-master/build/windows-x86_64-server-release/hotspot/variant-server/libjvm/objs/BUILD_LIBJVM_pch.cpp': 
> No such file or directory
> 
> The fix is to make sure WORKSPACE_ROOT in basics.m4 only gets values 
> that have been fixed using UTIL_FIXUP_PATH.
> 
> (This issue rarely occurs within Oracle, where Jib is already changing 
> the working to be on the /cygdrive format, which is why we haven't seen 
> it reported internally so far.)
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8249255
> 
> Webrev: http://cr.openjdk.java.net/~erikj/8249255/webrev.01/index.html
> 
> /Erik
>