The path to the rust source changes from 1.15 so preemptively make
changes to prepare for that.
Signed-off-by: Derek Straka <derek@asterius.io>
Signed-off-by: Doug Goldstein <cardoe@cardoe.com>
Redid how compiler-rt is built by using the Rust makefiles to build it
instead of compiler-rt's build system. Rust itself deviated from using
compiler-rt's build system and provided their own rules requiring the
source tree to be configured to use them.