libc: x86: Fixed size_t definition.

This patch changes the declaration of size_t on x86 targets
to test for the __ANDROID__ macro, instead of ANDROID

__ANDROID__ should be a builting toolchain macro, while ANDROID
is usually added manually during the build.

Testing against __ANDROID__ allows us to use the header when
using the NDK's standalone x86 toolchain.

This is related to http://code.google.com/p/android/issues/detail?id=19011
The bug was already fixed in the NDK platform headers, this simply updates
the C library one accordingly.

Change-Id: Ie038c4c8b37b7d24e2e4ae4d7a63371b69c9a51e

libc/arch-x86/include/machine/_types.h

@@ -38,7 +38,7 @@
 /* the kernel defines size_t as unsigned int, but g++ wants it to be unsigned long */
 #ifndef _SIZE_T_DEFINED_
 #  define _SIZE_T_DEFINED_
-#  ifdef ANDROID
+#  ifdef __ANDROID__
      typedef unsigned int  size_t;
 #  else
      typedef unsigned long  size_t;