Serialization: ensure that we deserialise IsStaticLibrary correctly

We would previously fail to deserialise the IsStaticLibrary bit on
certain declarations when they were imported implicitly.  This would
result in incorrect IRGen on Windows when building against a static
swift module.

Author: compnerd

lib/Serialization/DeserializeSIL.cpp

@@ -678,6 +678,7 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
     fn->setIsAlwaysWeakImported(isWeakImported);
     fn->setClassSubclassScope(SubclassScope(subclassScope));
     fn->setHasCReferences(bool(hasCReferences));
+    fn->setIsStaticallyLinked(MF->getAssociatedModule()->isStaticLibrary());
 
     llvm::VersionTuple available;
     DECODE_VER_TUPLE(available);

test/IRGen/static-serialization.swift

@@ -0,0 +1,19 @@
+// RUN: %empty-directory(%t)
+// RUN: %swift-target-frontend -static -emit-module -emit-module-path %t/StaticLibrary.swiftmodule/%host_triple.swiftmodule -module-name StaticLibrary -DSTATIC_LIBRARY %s
+// RUN: %swift-target-frontend -I%t -S %s -emit-ir -o - | %FileCheck %s
+
+#if STATIC_LIBRARY
+public final class S {
+    public init() { }
+    deinit {}
+}
+
+@_transparent
+public func f() -> S { S() }
+#else
+import StaticLibrary
+internal let s = f()
+#endif
+
+// CHECK-NOT: declare dllimport swiftcc ptr @"$s13StaticLibrary1SCACycfC"(ptr swiftself)
+// CHECK: declare swiftcc ptr @"$s13StaticLibrary1SCACycfC"(ptr swiftself)