message: repl: make the sources more portable to cl
  This allows us to build with cl as well as as clang.  Furthermore, it
  allows building on Windows.  A follow up change would actually load the
  swiftCore DLL.
diff: #include <dlfcn.h>
  #endif
  -#ifdef __gnu_linux__
  +#if defined(__linux__)
  #include <dlfcn.h>
  #endif
  #define REPL_MAIN _TF10repl_swift9repl_mainFT_Si
  -__attribute__((optnone))
  +#if !defined(__has_attribute)
  +#define __has_attribute(attribute) 0
  +#endif
  +
  +#if __has_attribute(__optnone__)
  +#define SWIFT_REPL_NOOPT __attribute__((__optnone__))
  +#else
  +#define SWIFT_REPL_NOOPT
  +#endif
  +
  +SWIFT_REPL_NOOPT
  int REPL_MAIN() {
  return 0;
  }
  -__attribute__((optnone))
  +SWIFT_REPL_NOOPT
  int main() {
  #ifdef __APPLE__
  // Force loading of libswiftCore.dylib, which is not linked at build time.
  dlopen("@rpath/libswiftCore.dylib", RTLD_LAZY);
  -#else
  +#elif defined(__linux__)
  dlopen("libswiftCore.so", RTLD_LAZY);
  #endif
  