attributes: drop pointless define guards

the av_-prefixed attributes must not be defined outside of this file

libavutil/attributes.h

@@ -32,7 +32,6 @@
 #    define AV_GCC_VERSION_AT_LEAST(x,y) 0
 #endif
 
-#ifndef av_always_inline
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define av_always_inline __attribute__((always_inline)) inline
 #elif defined(_MSC_VER)
@@ -40,92 +39,71 @@
 #else
 #    define av_always_inline inline
 #endif
-#endif
 
-#ifndef av_noinline
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define av_noinline __attribute__((noinline))
 #else
 #    define av_noinline
 #endif
-#endif
 
-#ifndef av_pure
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define av_pure __attribute__((pure))
 #else
 #    define av_pure
 #endif
-#endif
 
-#ifndef av_const
 #if AV_GCC_VERSION_AT_LEAST(2,6)
 #    define av_const __attribute__((const))
 #else
 #    define av_const
 #endif
-#endif
 
-#ifndef av_cold
 #if AV_GCC_VERSION_AT_LEAST(4,3)
 #    define av_cold __attribute__((cold))
 #else
 #    define av_cold
 #endif
-#endif
 
-#ifndef av_flatten
 #if AV_GCC_VERSION_AT_LEAST(4,1)
 #    define av_flatten __attribute__((flatten))
 #else
 #    define av_flatten
 #endif
-#endif
 
-#ifndef attribute_deprecated
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define attribute_deprecated __attribute__((deprecated))
 #else
 #    define attribute_deprecated
 #endif
-#endif
 
-#ifndef av_unused
 #if defined(__GNUC__)
 #    define av_unused __attribute__((unused))
 #else
 #    define av_unused
 #endif
-#endif
 
 /**
  * Mark a variable as used and prevent the compiler from optimizing it
  * away.  This is useful for variables accessed only from inline
  * assembler without the compiler being aware.
  */
-#ifndef av_used
 #if AV_GCC_VERSION_AT_LEAST(3,1)
 #    define av_used __attribute__((used))
 #else
 #    define av_used
 #endif
-#endif
 
-#ifndef av_alias
 #if AV_GCC_VERSION_AT_LEAST(3,3)
 #   define av_alias __attribute__((may_alias))
 #else
 #   define av_alias
 #endif
-#endif
 
-#ifndef av_uninit
 #if defined(__GNUC__) && !defined(__ICC)
 #    define av_uninit(x) x=x
 #else
 #    define av_uninit(x) x
 #endif
-#endif
 
 #ifdef __GNUC__
 #    define av_builtin_constant_p __builtin_constant_p