Add run-make-fulldeps test case

src/test/run-make-fulldeps/redundant-libs/Makefile

@@ -0,0 +1,11 @@
+-include ../tools.mk
+RUSTC_FLAGS = \
+    -l static=bar \
+    -l foo \
+    -l static=baz \
+    -l foo \
+    -Z print-link-args
+
+all: $(call DYLIB,foo) $(call STATICLIB,bar) $(call STATICLIB,baz)
+	$(RUSTC) $(RUSTC_FLAGS) main.rs
+	$(call RUN,main)

src/test/run-make-fulldeps/redundant-libs/bar.c

@@ -0,0 +1,12 @@
+// Copyright 2019 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.
+
+void bar() {
+}

src/test/run-make-fulldeps/redundant-libs/baz.c

@@ -0,0 +1,17 @@
+// Copyright 2019 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.
+
+extern void foo1();
+extern void foo2();
+
+void baz() {
+  foo1();
+  foo2();
+}

src/test/run-make-fulldeps/redundant-libs/foo.c

@@ -0,0 +1,12 @@
+// Copyright 2019 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.
+
+void foo1() {}
+void foo2() {}

src/test/run-make-fulldeps/redundant-libs/main.rs

@@ -0,0 +1,30 @@
+// Copyright 2019 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.
+
+// rustc will remove one of the two redundant references to foo below.  Depending on which one gets
+// removed, we'll get a linker error on SOME platforms (like Linux).  On these platforms, when a
+// library is referenced, the linker will only pull in the symbols needed _at that point in time_.
+// If a later library depends on additional symbols from the library, they will not have been
+// pulled in, and you'll get undefined symbols errors.
+//
+// So in this example, we need to ensure that rustc keeps the _later_ reference to foo, and not the
+// former one.
+
+extern "C" {
+    fn bar();
+    fn baz();
+}
+
+fn main() {
+    unsafe {
+        bar();
+        baz();
+    }
+}