Only build aom_read/write_symbol if CONFIG_EC_MULTISYMBOL

Change-Id: If86c7220ac9199a59e605dc43d42cc3db26cf8bd

aom_dsp/bitreader.h

diff --git a/aom_dsp/bitreader.h b/aom_dsp/bitreader.h
index 3907849..00ea158 100644
--- a/aom_dsp/bitreader.h
+++ b/aom_dsp/bitreader.h
@@ -203,6 +203,7 @@
   return ret;
 }
 
+#if CONFIG_EC_MULTISYMBOL
 static INLINE int aom_read_symbol_(aom_reader *r, aom_cdf_prob *cdf,
                                    int nsymbs ACCT_STR_PARAM) {
   int ret;
@@ -212,12 +213,11 @@
 #elif CONFIG_DAALA_EC
   ret = daala_read_symbol(r, cdf, nsymbs);
 #else
-  (void)r;
-  (void)cdf;
-  (void)nsymbs;
-  assert(0 && "Unsupported bitreader operation");
-  ret = -1;
+#error \
+    "CONFIG_EC_MULTISYMBOL is selected without a valid backing entropy " \
+  "coder. Enable daala_ec or ans for a valid configuration."
 #endif
+
 #if CONFIG_EC_ADAPT
   update_cdf(cdf, ret, nsymbs);
 #endif
@@ -227,6 +227,7 @@
 #endif
   return ret;
 }
+#endif  // CONFIG_EC_MULTISYMBOL
 
 #ifdef __cplusplus
 }  // extern "C"

aom_dsp/bitwriter.h

diff --git a/aom_dsp/bitwriter.h b/aom_dsp/bitwriter.h
index 4ece930..7fcd9e9 100644
--- a/aom_dsp/bitwriter.h
+++ b/aom_dsp/bitwriter.h
@@ -98,6 +98,7 @@
 #endif
 }
 
+#if CONFIG_EC_MULTISYMBOL
 static INLINE void aom_write_symbol(aom_writer *w, int symb, aom_cdf_prob *cdf,
                                     int nsymbs) {
 #if CONFIG_RANS
@@ -110,17 +111,16 @@
 #elif CONFIG_DAALA_EC
   daala_write_symbol(w, symb, cdf, nsymbs);
 #else
-  (void)w;
-  (void)symb;
-  (void)cdf;
-  (void)nsymbs;
-  assert(0 && "Unsupported bitwriter operation");
+#error \
+    "CONFIG_EC_MULTISYMBOL is selected without a valid backing entropy " \
+  "coder. Enable daala_ec or ans for a valid configuration."
 #endif
 
 #if CONFIG_EC_ADAPT
   update_cdf(cdf, symb, nsymbs);
 #endif
 }
+#endif  // CONFIG_EC_MULTISYMBOL
 
 #ifdef __cplusplus
 }  // extern "C"