Add test to check for fmt::write bloat.

It checks that fmt::write by itself doesn't pull in any panicking or
or display code.

src/test/run-make/fmt-write-bloat/Makefile

@@ -0,0 +1,25 @@
+-include ../../run-make-fulldeps/tools.mk
+
+# ignore-windows
+
+ifeq ($(shell $(RUSTC) -vV | grep 'host: $(TARGET)'),)
+
+# Don't run this test when cross compiling.
+all:
+
+else
+
+NM = nm
+
+PANIC_SYMS = panic_bounds_check pad_integral Display Debug
+
+# Allow for debug_assert!() in debug builds of std.
+ifdef NO_DEBUG_ASSERTIONS
+PANIC_SYMS += panicking panic_fmt
+endif
+
+all: main.rs
+	$(RUSTC) $< -O
+	$(NM) $(call RUN_BINFILE,main) | $(CGREP) -v $(PANIC_SYMS)
+
+endif

src/test/run-make/fmt-write-bloat/main.rs

@@ -0,0 +1,32 @@
+#![feature(lang_items)]
+#![feature(start)]
+#![no_std]
+
+use core::fmt;
+use core::fmt::Write;
+
+#[link(name = "c")]
+extern "C" {}
+
+struct Dummy;
+
+impl fmt::Write for Dummy {
+    #[inline(never)]
+    fn write_str(&mut self, _: &str) -> fmt::Result {
+        Ok(())
+    }
+}
+
+#[start]
+fn main(_: isize, _: *const *const u8) -> isize {
+    let _ = writeln!(Dummy, "Hello World");
+    0
+}
+
+#[lang = "eh_personality"]
+fn eh_personality() {}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}