Add test of --print + -o

Author: dtolnay

tests/run-make/print-cfg/Makefile

@@ -2,7 +2,7 @@
 
 include ../tools.mk
 
-all: default
+all: default output_to_file
 	$(RUSTC) --target x86_64-pc-windows-gnu --print cfg | $(CGREP) windows
 	$(RUSTC) --target x86_64-pc-windows-gnu --print cfg | $(CGREP) x86_64
 	$(RUSTC) --target i686-pc-windows-msvc --print cfg | $(CGREP) msvc
@@ -11,6 +11,14 @@ all: default
 	$(RUSTC) --target arm-unknown-linux-gnueabihf --print cfg | $(CGREP) target_abi=
 	$(RUSTC) --target arm-unknown-linux-gnueabihf --print cfg | $(CGREP) eabihf
 
+output_to_file:
+	-rm $(TMPDIR)/cfg.txt
+	$(RUSTC) --target x86_64-pc-windows-gnu --print=cfg -o $(TMPDIR)/cfg.txt
+	$(CGREP) windows < $(TMPDIR)/cfg.txt
+	-rm $(TMPDIR)/cfg.txt
+	$(RUSTC) --target x86_64-pc-windows-gnu --print=target-cpus -o $(TMPDIR)/cfg.txt
+	$(CGREP) native < $(TMPDIR)/cfg.txt
+
 ifdef IS_WINDOWS
 default:
 	$(RUSTC) --print cfg | $(CGREP) windows