LAKITU: Set EGIT_MASTER=main for more llvm packages

My previous commit missed some LLVM packages. We need to fix these too.

BUG=b/178727618
TEST=emerge-lakitu llvm-libunwind, emerge-lakitu compiler-rt
RELEASE_NOTE=None

Change-Id: I00ebe101a65376b8bb4326804d0b41c907e58ed9
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/11592
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Anil Altinay <aaltinay@google.com>