Add support for "-fdebug-prefix-map" to make debugging easier

[JCash]

Instead of having the random job folder as part of the file paths, we can substitute it with either:

• /tmp/job123456 -> /extender/build/
  • Good for caching, and everyone gets the same paths
  • Still has to setup debug mappings locally
• /tmp/job123456 -> /path/to/user/project
  • Good for user
  • Our caching will not work across users

From gcc:

"
-fdebug-prefix-map=old=new

When compiling files residing in directory old, record debugging information describing them as if the files resided in directory new instead. This can be used to replace a build-time path with an install-time path in the debug info. It can also be used to change an absolute path to a relative path by using . for new. This can give more reproducible builds, which are location independent, but may require an extra command to tell GDB where to find the source files. See also -ffile-prefix-map.
"