This commit imports libcore 1.49.0 into a new directory,
"libgrust/rustc-lib/core". LICENSE-* files are taken from the rustc
1.49.0 repository root.
libgrust/ChangeLog:
* rustc-lib/LICENSE-APACHE: New file.
* rustc-lib/LICENSE-MIT: New file.
* rustc-lib/version-info: New file.
Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>