IRGen: give the force load symbol export DLL storage

The force load symbol was not marked as DLL export.  This would result in the
symbol not being emitted into the import library and consequently not being
available to the consumer.  This ensures that the symbol is visible outside of
the module.

Author: compnerd

lib/IRGen/IRGenModule.cpp

@@ -975,10 +975,13 @@ void IRGenModule::emitAutolinkInfo() {
   if (!IRGen.Opts.ForceLoadSymbolName.empty()) {
     llvm::SmallString<64> buf;
     encodeForceLoadSymbolName(buf, IRGen.Opts.ForceLoadSymbolName);
-    (void)new llvm::GlobalVariable(Module, Int1Ty, /*constant=*/false,
-                                   llvm::GlobalValue::CommonLinkage,
-                                   llvm::Constant::getNullValue(Int1Ty),
-                                   buf.str());
+    auto symbol =
+        new llvm::GlobalVariable(Module, Int1Ty, /*constant=*/false,
+                                 llvm::GlobalValue::CommonLinkage,
+                                 llvm::Constant::getNullValue(Int1Ty),
+                                 buf.str());
+    if (Triple.isOSBinFormatCOFF())
+      symbol->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
   }
 }
 

test/IRGen/autolink-coff-force-link.swift

@@ -0,0 +1,11 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+
+// RUN: %swift -target i686--windows-msvc -parse-as-library -parse-stdlib -module-name autolink -module-link-name autolink -autolink-force-load -emit-ir -o - %s | FileCheck %s
+// RUN: %swift -target i686--windows-itanium -parse-as-library -parse-stdlib -module-name autolink -module-link-name autolink -autolink-force-load -S -o - %s | FileCheck %s -check-prefix CHECK-ASM-GNU
+// RUN: %swift -target i686--windows-msvc -parse-as-library -parse-stdlib -module-name autolink -module-link-name autolink -autolink-force-load -S -o - %s | FileCheck %s -check-prefix CHECK-ASM-MSC
+
+// CHECK: @"_swift_FORCE_LOAD_$_autolink" = common dllexport global i1 false
+// CHECK-ASM-GNU: .ascii  " -export:__swift_FORCE_LOAD_$_autolink,data"
+// CHECK-ASM-MSC: .ascii  " /EXPORT:__swift_FORCE_LOAD_$_autolink,DATA"
+