[Test Only] Add a test for correctly querying Clang global variable linkage when using '-clang-target'

Author: artemcm

test/SILGen/clang-target-weak-import-globalvar.swift

@@ -0,0 +1,69 @@
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/module-cache)
+// RUN: %empty-directory(%t/deps)
+// RUN: %empty-directory(%t/inputs)
+// RUN: split-file %s %t
+
+// - Prepare the explicit input map
+// RUN: sed -e "s|INPUTSDIR|%/t/inputs|g" %t/map.json.template > %t/map.json.template1
+// RUN: sed -e "s|STDLIBMOD|%/stdlib_module|g" %t/map.json.template1 > %t/map.json.template2
+// RUN: sed -e "s|ONONEMOD|%/ononesupport_module|g" %t/map.json.template2 > %t/map.json.template3
+// RUN: sed -e "s|CHEADERSDIR|%t/deps|g" %t/map.json.template3 > %t/map.json.template4
+// RUN: sed -e "s|SWIFTLIBDIR|%swift-lib-dir|g" %t/map.json.template4 > %t/map.json
+
+// - Set up explicit dependencies for the client
+// RUN: %target-swift-emit-pcm -module-name SwiftShims %swift-lib-dir/swift/shims/module.modulemap -o %t/inputs/SwiftShims.pcm -target %target-cpu-apple-macosx26.0 -Xcc -Xclang -Xcc -fbuiltin-headers-in-system-modules
+// RUN: %target-swift-emit-pcm -module-name Foo %t/deps/module.modulemap -o %t/inputs/Foo.pcm -target %target-cpu-apple-macosx26.0 -Xcc -Xclang -Xcc -fbuiltin-headers-in-system-modules
+
+// - Build the client
+// RUN: %target-swift-frontend -c %t/client.swift -explicit-swift-module-map-file %t/map.json -disable-implicit-swift-modules -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -o %t/client.o -target %target-cpu-apple-macosx15.5 -clang-target %target-cpu-apple-macosx26.0  -Xcc -Xclang -Xcc -fbuiltin-headers-in-system-modules
+
+// - Ensure that the client's code-gen treats 'brandNewInteger' as a weak external symbol
+// RUN: %llvm-nm -m %t/client.o | %FileCheck %s
+// CHECK: (undefined) weak external _brandNewInteger
+
+//--- deps/Foo.h
+__attribute__((availability(macosx,introduced=26.0)))
+__attribute__((visibility("default")))
+const extern void* __nonnull brandNewInteger;
+
+//--- deps/module.modulemap
+module Foo {
+    header "Foo.h"
+    export *
+}
+
+//--- map.json.template
+[
+  {
+      "moduleName": "Foo",
+      "clangModulePath": "INPUTSDIR/Foo.pcm",
+      "clangModuleMapPath": "CHEADERSDIR/module.modulemap"
+  },
+  {
+      "moduleName": "Swift",
+      "modulePath": "STDLIBMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftOnoneSupport",
+      "modulePath": "ONONEMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftShims",
+      "isFramework": false,
+      "clangModuleMapPath": "SWIFTLIBDIR/swift/shims/module.modulemap",
+      "clangModulePath": "INPUTSDIR/SwiftShims.pcm"
+}]
+
+
+//--- client.swift
+import Foo
+func f() {
+	if #available(macOS 26.0, *) {
+		print(brandNewInteger)
+	}
+}