[m-rev.] diff: use cast to union type extension with clang

[Julien Fischer]

Use GCC's cast to union extension with clang.

runtime/mercury_float.h:
 	Define MR_float_to_word and MR_word_to_float as macros using GCC's
 	cast to union extension with clang, since it also supports that
 	extension.

Julien.

diff --git a/runtime/mercury_float.h b/runtime/mercury_float.h
index 9009593..7c40298 100644
--- a/runtime/mercury_float.h
+++ b/runtime/mercury_float.h
@@ -167,22 +167,25 @@

    #define MR_float_const(f) MR_float_to_word(f)

-  #ifdef MR_GNUC
+  #if defined(MR_GNUC) || defined(MR_CLANG)

-    /* GNU C allows you to cast to a union type */
+    /*
+    ** GNU C allows you to cast to a union type.
+    ** clang also provides this extension.
+    */
      #define MR_float_to_word(f) (__extension__ \
                                  ((union MR_Float_Word)(MR_Float)(f)).w)
      #define MR_word_to_float(w) (__extension__ \
                                  ((union MR_Float_Word)(MR_Word)(w)).f)

-  #else /* not MR_GNUC */
+  #else /* not MR_GNUC or MR_CLANG */

      static MR_Word MR_float_to_word(MR_Float f)
          { union MR_Float_Word tmp; tmp.f = f; return tmp.w; }
      static MR_Float MR_word_to_float(MR_Word w)
          { union MR_Float_Word tmp; tmp.w = w; return tmp.f; }

-  #endif /* not MR_GNUC */
+  #endif /* not MR_GNUC or MR_CLANG */

  #endif /* not MR_BOXED_FLOAT */