Resolve compiler warning when highbd is off

The highbd_clip_pixel_add() function is generalized to be used in
the regular 8 bit path. Move its defintions outside the highbd
experimental flag.

This resolves the comiler warning in unit tests when high bit-depth
is turned off.

Change-Id: I90a744adb2381c9bf8476aa2a2bd0c87d9afdf57

aom_dsp/aom_dsp_common.h

diff --git a/aom_dsp/aom_dsp_common.h b/aom_dsp/aom_dsp_common.h
index d879ec0..fb363fd 100644
--- a/aom_dsp/aom_dsp_common.h
+++ b/aom_dsp/aom_dsp_common.h
@@ -91,7 +91,6 @@
   return value < low ? low : (value > high ? high : value);
 }
 
-#if CONFIG_HIGHBITDEPTH
 static INLINE uint16_t clip_pixel_highbd(int val, int bd) {
   switch (bd) {
     case 8:
@@ -100,7 +99,6 @@
     case 12: return (uint16_t)clamp(val, 0, 4095);
   }
 }
-#endif  // CONFIG_HIGHBITDEPTH
 
 #ifdef __cplusplus
 }  // extern "C"

aom_dsp/inv_txfm.h

diff --git a/aom_dsp/inv_txfm.h b/aom_dsp/inv_txfm.h
index e64d463..3ec59fe 100644
--- a/aom_dsp/inv_txfm.h
+++ b/aom_dsp/inv_txfm.h
@@ -51,9 +51,7 @@
 }
 
 #define WRAPLOW(x) ((int32_t)check_range(x, 8))
-#if CONFIG_HIGHBITDEPTH
 #define HIGHBD_WRAPLOW(x, bd) ((int32_t)check_range((x), bd))
-#endif  // CONFIG_HIGHBITDEPTH
 
 void aom_idct4_c(const tran_low_t *input, tran_low_t *output);
 void aom_idct8_c(const tran_low_t *input, tran_low_t *output);
@@ -72,13 +70,13 @@
 void aom_highbd_iadst4_c(const tran_low_t *input, tran_low_t *output, int bd);
 void aom_highbd_iadst8_c(const tran_low_t *input, tran_low_t *output, int bd);
 void aom_highbd_iadst16_c(const tran_low_t *input, tran_low_t *output, int bd);
+#endif  // CONFIG_HIGHBITDEPTH
 
 static INLINE uint16_t highbd_clip_pixel_add(uint16_t dest, tran_high_t trans,
                                              int bd) {
   trans = HIGHBD_WRAPLOW(trans, bd);
   return clip_pixel_highbd(dest + (int)trans, bd);
 }
-#endif
 
 static INLINE uint8_t clip_pixel_add(uint8_t dest, tran_high_t trans) {
   trans = WRAPLOW(trans);