ld_bfd: set env var to appease ChromeOS checks

Without this env var (or a similar argv), ChromeOS' Clang and LLD will
start breaking. ChromeOS is aware of these uses of its toolchain, so
preemptively opt out.

Bug: b:396436337, b:397463803
Change-Id: I3f9a32c15e2ff03a5ce513013cf8403352b11643
Reviewed-on: https://chromium-review.googlesource.com/c/native_client/src/native_client/+/6479405
Reviewed-by: Mark Seaborn <mseaborn@chromium.org>

src/trusted/service_runtime/linux/ld_bfd.py

diff --git a/src/trusted/service_runtime/linux/ld_bfd.py b/src/trusted/service_runtime/linux/ld_bfd.py
index c727e96..7385e28 100755
--- a/src/trusted/service_runtime/linux/ld_bfd.py
+++ b/src/trusted/service_runtime/linux/ld_bfd.py
@@ -53,6 +53,10 @@
 
 
 def main(args):
+  # b/397463803: Set this until CrOS' user enumeration is done; its `clang` will
+  # error out otherwise.
+  os.environ["CROSTC_IS_AWARE_OF_THIS_USECASE"] = "1"
+
   # Find path to compiler, either from the command line or the environment,
   # falling back to just 'g++'
   if '--compiler' in args: