Upgrade arm-none-eabi compiler

It was 5 years out of date and didn't fully support C++20.

In doing so, flip off "freestanding" mode for the cortex-m4f compiler's
use of libstdc++.
This is because some libraries appear to have been using STL headers
that cannot be safely linked against in freestanding mode (e.g.,
<ostream>). I am unsure why the prior compiler was not catching this.
If this becomes a problem, we can disable it.

Change-Id: Ie08ce2c089f787b0433a761ad2242dcd2a516404
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/build_tests/BUILD b/build_tests/BUILD
index c097726..f0ff94d 100644
--- a/build_tests/BUILD
+++ b/build_tests/BUILD
@@ -213,6 +213,7 @@
     srcs = [
         "upstream_python_test.py",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "@pip//matplotlib",
         "@pip//numpy",