cros_setup_toolchains: Build compiler-rt in armv7m-cros-eabi.

We want to provide compiler-rt libraries in armv7m toolchain.
So add armv7m-cros-eabi to compiler-rt list.

BUG=chromium:819464
TEST=cros_setup_toolchains -t armv7m-cros-eabi --nousepkg installs
     compiler-rt.

Change-Id: I87069562a9ed7b7b5204105f73582a821e895411
Reviewed-on: https://chromium-review.googlesource.com/952044
Commit-Ready: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 64b8825..34ce84a 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -90,6 +90,7 @@
     'armv7a-cros-linux-gnueabi',
     'armv7a-cros-linux-gnueabihf',
     'aarch64-cros-linux-gnu',
+    'armv7m-cros-eabi',
 )
 CROSSDEV_COMPILER_RT_ARGS = ['--ex-pkg', 'sys-libs/compiler-rt']