inline vpx functions in headers to avoid unused function warning

Change-Id: I80284ae82915b9df56f7c5ef4953bd53e8cffd1f
diff --git a/vpx/vpx_integer.h b/vpx/vpx_integer.h
index 258618b..ffeefb8 100644
--- a/vpx/vpx_integer.h
+++ b/vpx/vpx_integer.h
@@ -15,6 +15,15 @@
 /* get ptrdiff_t, size_t, wchar_t, NULL */
 #include <stddef.h>
 
+#if defined(_MSC_VER)
+#define VPX_FORCE_INLINE __forceinline
+#define VPX_INLINE __inline
+#else
+#define VPX_FORCE_INLINE __inline__ __attribute__(always_inline)
+// TODO(jbb): Allow a way to force inline off for older compilers.
+#define VPX_INLINE inline
+#endif
+
 #if (defined(_MSC_VER) && (_MSC_VER < 1600)) || defined(VPX_EMULATE_INTTYPES)
 typedef signed char  int8_t;
 typedef signed short int16_t;