Add test for Apple's -weak_framework linker argument

Author: madsmtm

tests/run-pass-valgrind/osx-frameworks.rs

@@ -0,0 +1,12 @@
+error: linking with `cc` failed: exit status: 1
+   |
+   = note: [linker command]
+   = note: ld: warning: search path '$TEST_BUILD_DIR/linkage-attr/framework.omit/auxiliary' not found
+           ld: Undefined symbols:
+             _CFRunLoopGetTypeID, referenced from:
+                 framework::main::HASH in framework.framework.HASH-cgu.0.rcgu.o
+           clang: error: linker command failed with exit code 1 (use -v to see invocation)
+           
+
+error: aborting due to 1 previous error
+

tests/ui/linkage-attr/framework.omit.stderr

@@ -0,0 +1,23 @@
+// Check linking frameworks on Apple platforms works.
+// only-macos
+// revisions: omit link weak
+// [omit]build-fail
+// [link]run-pass
+// [weak]run-pass
+// normalize-stderr-test: "note: env .*" -> "note: [linker command]"
+// normalize-stderr-test: "framework::main::\w* in framework\.framework\.\w*-cgu\.0\.rcgu\.o" -> "framework::main::HASH in framework.framework.HASH-cgu.0.rcgu.o"
+
+#![cfg_attr(weak, feature(link_arg_attribute))]
+
+#[cfg_attr(link, link(name = "CoreFoundation", kind = "framework"))]
+#[cfg_attr(weak, link(name = "-weak_framework", kind = "link-arg", modifiers = "+verbatim"))]
+#[cfg_attr(weak, link(name = "CoreFoundation", kind = "link-arg", modifiers = "+verbatim"))]
+extern "C" {
+    fn CFRunLoopGetTypeID() -> core::ffi::c_ulong;
+}
+
+pub fn main() {
+    unsafe {
+        CFRunLoopGetTypeID();
+    }
+}