Prevent rustc overwriting input files

If rustc is invoked on a file that would be overwritten by the
compilation, the compilation now fails, to avoid accidental loss. This
resolves #13019.

src/test/run-make/output-filename-overwrites-input/Makefile

@@ -0,0 +1,10 @@
+-include ../tools.mk
+
+all:
+	cp foo.rs $(TMPDIR)/foo
+	$(RUSTC) $(TMPDIR)/foo 2>&1 \
+		| $(CGREP) -e "the input file \".*foo\" would be overwritten by the generated executable"
+	$(RUSTC) foo.rs 2>&1 && $(RUSTC) -Z ls $(TMPDIR)/foo 2>&1
+	cp foo.rs $(TMPDIR)/foo.rs
+	$(RUSTC) $(TMPDIR)/foo.rs -o $(TMPDIR)/foo.rs 2>&1 \
+		| $(CGREP) -e "the input file \".*foo.rs\" would be overwritten by the generated executable"

src/test/run-make/output-filename-overwrites-input/foo.rs

@@ -0,0 +1,11 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {}

src/test/run-make/weird-output-filenames/Makefile

@@ -7,8 +7,8 @@ all:
 	cp foo.rs $(TMPDIR)/.foo.bar
 	$(RUSTC) $(TMPDIR)/.foo.bar 2>&1 \
 		| $(CGREP) -e "invalid character.*in crate name:"
-	cp foo.rs $(TMPDIR)/+foo+bar
-	$(RUSTC) $(TMPDIR)/+foo+bar 2>&1 \
+	cp foo.rs $(TMPDIR)/+foo+bar.rs
+	$(RUSTC) $(TMPDIR)/+foo+bar.rs 2>&1 \
 		| $(CGREP) -e "invalid character.*in crate name:"
 	cp foo.rs $(TMPDIR)/-foo.rs
 	$(RUSTC) $(TMPDIR)/-foo.rs 2>&1 \