We should be always rebasing paths against root_build_dir which is
the directory where scripts are run from, not root_out_dir which is
the current toolchain directory. The latter can result in invalid
paths when the action is being used from a non-default toolchain.
Differential Revision: https://reviews.llvm.org/D60330
llvm-svn: 357798
This is slightly involved, see the comments in the code.
The GN build now builds a functional lld!
Differential Revision: https://reviews.llvm.org/D55606
llvm-svn: 349096