Update mips64el_toolchain_linux to GCC 7

Change-Id: I31f4f2aff4e35dac066d208a9048ab0f96020fd1
Reviewed-on: https://skia-review.googlesource.com/118681
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
2 files changed