cmd/compile: rename internal-abi.md to abi-internal.md

Allows muscle-memoried tab completion of cmd/compile/internal/...
paths to work again.

Change-Id: Ib54a5f2cc9fabcb876c2e62635828ab28b565501
Reviewed-on: https://go-review.googlesource.com/c/go/+/299530
Reviewed-by: Austin Clements <austin@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/compile/internal-abi.md b/src/cmd/compile/abi-internal.md
similarity index 100%
rename from src/cmd/compile/internal-abi.md
rename to src/cmd/compile/abi-internal.md