externals: Search for shared opus installation.

We had used conan for opus before, but there was a bug in the AVX detection.
However we still had the Findopus.cmake file within the repository, but not used.

This patch reenables the Findopus helper and prefer the system wide installation of opus.

externals/CMakeLists.txt

@@ -97,4 +97,8 @@ if (ENABLE_WEB_SERVICE)
 endif()
 
 # Opus
-add_subdirectory(opus)
+find_package(opus 1.3)
+if (NOT opus_FOUND)
+    message(STATUS "opus 1.3 or newer not found, falling back to externals")
+    add_subdirectory(opus EXCLUDE_FROM_ALL)
+endif()

externals/find-modules/Findopus.cmake

@@ -28,7 +28,7 @@ if(opus_FOUND)
 endif()
 
 if(opus_FOUND AND NOT TARGET Opus::Opus)
-  add_library(Opus::Opus UNKNOWN IMPORTED)
+  add_library(Opus::Opus UNKNOWN IMPORTED GLOBAL)
   set_target_properties(Opus::Opus PROPERTIES
     IMPORTED_LOCATION "${opus_LIBRARY}"
     INTERFACE_COMPILE_OPTIONS "${PC_opus_CFLAGS_OTHER}"

externals/opus/CMakeLists.txt

@@ -252,3 +252,5 @@ PRIVATE
     opus/silk/float
     opus/src
 )
+
+add_library(Opus::Opus ALIAS opus)