Add an option that allows us to specify that we require toxav.

CMakeLists.txt

@@ -188,16 +188,23 @@ if(NOT USE_IPV6)
 endif()
 
 option(BUILD_TOXAV "Whether to build the tox AV library" ON)
+option(MUST_BUILD_TOXAV "Fail the build if toxav cannot be built" OFF)
 
 include(Dependencies)
 
+if(MUST_BUILD_TOXAV)
+  set(NO_TOXAV_ERROR_TYPE SEND_ERROR)
+else()
+  set(NO_TOXAV_ERROR_TYPE WARNING)
+endif()
+
 if(BUILD_TOXAV)
   if(NOT OPUS_FOUND)
-    message(WARNING "Option BUILD_TOXAV is enabled but required library OPUS was not found.")
+    message(${NO_TOXAV_ERROR_TYPE} "Option BUILD_TOXAV is enabled but required library OPUS was not found.")
     set(BUILD_TOXAV OFF)
   endif()
   if(NOT VPX_FOUND)
-    message(WARNING "Option BUILD_TOXAV is enabled but required library VPX was not found.")
+    message(${NO_TOXAV_ERROR_TYPE} "Option BUILD_TOXAV is enabled but required library VPX was not found.")
     set(BUILD_TOXAV OFF)
   endif()
 endif()

other/travis/toxcore-script

@@ -30,6 +30,7 @@ RUN $CMAKE                                      \
   -DCMAKE_INSTALL_PREFIX:PATH=$CURDIR/_install  \
   -DASAN=ON                                     \
   -DDEBUG=ON                                    \
+  -DMUST_BUILD_TOXAV=ON                         \
   -DSTRICT_ABI=ON                               \
   -DTEST_TIMEOUT_SECONDS=120                    \
   -DTRACE=ON                                    \