add test for issue #21335

Fixes #21335.

Author: euclio

src/test/run-make/llvm-outputs/Makefile

@@ -0,0 +1,5 @@
+-include ../../run-make-fulldeps/tools.mk
+
+all:
+	echo 'fn main() {}' | $(BARE_RUSTC) - --out-dir=$(TMPDIR)/random_directory_that_does_not_exist_ir/ --emit=llvm-ir
+	echo 'fn main() {}' | $(BARE_RUSTC) - --out-dir=$(TMPDIR)/random_directory_that_does_not_exist_bc/ --emit=llvm-bc