ClangImporter: import SwiftShims properly for static linking

When building against the static standard library, we should define
`SWIFT_STATIC_STDLIB` to indicate to the shims that the declarations
should be giving hidden visibility and default DLL storage. This is
required to ensure that these symbols are known to be `dso_local` when
compiling to avoid an unnecessary look up through the PLT/GOT or the
indirection through the synthesized `__imp_` symbol and the IAT. This
corrects a number of incorrect code generation cases on Windows with the
static standard library.

Author: compnerd

include/swift/Basic/LangOptions.h

@@ -321,6 +321,8 @@ namespace swift {
     /// Flags for use by tests
     ///
 
+    bool UseStaticStandardLibrary = false;
+
     /// Enable Objective-C Runtime interop code generation and build
     /// configuration options.
     bool EnableObjCInterop = true;

lib/ClangImporter/ClangImporter.cpp

@@ -682,6 +682,9 @@ void importer::getNormalInvocationArguments(
     }
   }
 
+  if (LangOpts.UseStaticStandardLibrary)
+    invocationArgStrs.push_back("-DSWIFT_STATIC_STDLIB");
+
   // If we support SendingArgsAndResults, set the -D flag to signal that it
   // is supported.
   if (LangOpts.hasFeature(Feature::SendingArgsAndResults))

lib/Frontend/CompilerInvocation.cpp

@@ -1571,6 +1571,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     ModuleInterfaceOpts.PublicFlags.IgnorableFlags +=
         " " + printFormalCxxInteropVersion(Opts);
 
+  Opts.UseStaticStandardLibrary = Args.hasArg(OPT_use_static_resource_dir);
   Opts.EnableObjCInterop =
       Args.hasFlag(OPT_enable_objc_interop, OPT_disable_objc_interop,
                    Target.isOSDarwin() && !Opts.hasFeature(Feature::Embedded));

test/ClangImporter/static_stdlib.swift

@@ -0,0 +1,5 @@
+// RUN: %swift_frontend_plain -parse-stdlib -typecheck %s -dump-clang-diagnostics 2>&1 | %FileCheck %s -check-prefix CHECK-DYNAMIC
+// RUN: %swift_frontend_plain -parse-stdlib -use-static-resource-dir -typecheck %s -dump-clang-diagnostics 2>&1 | %FileCheck %s -check-prefix CHECK-STATIC
+
+// CHECK-DYNAMIC-NOT: clang importer cc1 args: {{.*}} '-D' 'SWIFT_STATIC_STDLIB'
+// CHECK-STATIC: clang importer cc1 args: {{.*}} '-D' 'SWIFT_STATIC_STDLIB'