There is a -Clinker='arm-none-eabi-gcc' that seems to be causing trouble.

Author: Tor Hovland

src/test/run-make/issue-10971-temps-dir/Makefile

@@ -3,6 +3,9 @@
 # Regression test for issue #10971
 # Running two invocations in parallel would overwrite each other's temp files.
 
+## clean up unused env variables which might cause harm.
+unexport RUSTC_LINKER
+
 all:
 	touch $(TMPDIR)/lib.rs