Add test case for https://bugs.swift.org/browse/SR-8963

I believe this was fixed by swiftlang#19825,
but this specific case with bitfield accessors is tricky so let's
test it explicity.

Author: slavapestov

test/ClangImporter/Inputs/inlinable_bitfields_other.swift

@@ -0,0 +1,9 @@
+import ctypes
+
+public struct MM {
+  public var m: ModRM
+}
+
+@inlinable public func f(_ m: MM) -> UInt32 {
+  return m.m.rm
+}

test/ClangImporter/inlinable_bitfields.swift

@@ -0,0 +1,13 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %clang-importer-sdk %S/Inputs/inlinable_bitfields_other.swift -emit-module -emit-module-path %t/inlinable_bitfields_other.swiftmodule
+// RUN: %target-swift-frontend %clang-importer-sdk -I %t %s -emit-ir -disable-llvm-optzns -O | %FileCheck %s -DINT=i%target-ptrsize
+
+import inlinable_bitfields_other
+
+public func g(_ m: MM) -> UInt32 {
+  return f(m)
+}
+
+// Just make sure this is a definition and not a declaration...
+
+// CHECK: define internal i32 @"$ModRM$rm$getter"([[INT]] %.coerce)