Add simple link_section test to exercise it

src/test/run-pass/link-section.rs

@@ -0,0 +1,34 @@
+#[cfg(not(target_os = "macos"))]
+#[link_section=".moretext"]
+fn i_live_in_more_text() -> &'static str {
+    "knock knock"
+}
+
+#[cfg(not(target_os = "macos"))]
+#[link_section=".imm"]
+static magic: uint = 42;
+
+#[cfg(not(target_os = "macos"))]
+#[link_section=".mut"]
+static mut frobulator: uint = 0xdeadbeef;
+
+#[cfg(target_os = "macos")]
+#[link_section="__TEXT,__moretext"]
+fn i_live_in_more_text() -> &'static str {
+    "knock knock"
+}
+
+#[cfg(target_os = "macos")]
+#[link_section="__RODATA,__imm"]
+static magic: uint = 42;
+
+#[cfg(target_os = "macos")]
+#[link_section="__DATA,__mut"]
+static mut frobulator: uint = 0xdeadbeef;
+
+fn main() {
+    unsafe {
+        frobulator = 0xcafebabe;
+        printfln!("%? %? %?", i_live_in_more_text(), magic, frobulator);
+    }
+}