Fix MANGLE macro on Mac OS X.

Allows compiling a 64 bit FFmpeg on Mac OS X without using --disable-mmx.
patch by İsmail Dönmez  ismail namtrac org

Originally committed as revision 12468 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/internal.h

@@ -120,7 +120,8 @@
 
 // Use rip-relative addressing if compiling PIC code on x86-64.
 #if defined(__MINGW32__) || defined(__CYGWIN__) || defined(__DJGPP__) || \
-    defined(__OS2__) || (defined (__OpenBSD__) && !defined(__ELF__))
+    defined(__OS2__) || defined(__APPLE__) || \
+    (defined (__OpenBSD__) && !defined(__ELF__))
 #    if defined(ARCH_X86_64) && defined(PIC)
 #        define MANGLE(a) "_" #a"(%%rip)"
 #    else
@@ -129,8 +130,6 @@
 #else
 #    if defined(ARCH_X86_64) && defined(PIC)
 #        define MANGLE(a) #a"(%%rip)"
-#    elif defined(__APPLE__)
-#        define MANGLE(a) "_" #a
 #    else
 #        define MANGLE(a) #a
 #    endif