cmake: Avoid breaking ABI through major version bump on Linux

Freeze SOVERSION to 30, this number is to be incremented when a clean
break is wanted.

cmake/linux/helpers.cmake

@@ -59,8 +59,8 @@ function(set_target_properties_obs target)
     set_target_properties(
       ${target}
       PROPERTIES
-        VERSION ${OBS_VERSION_CANONICAL}
-        SOVERSION ${OBS_VERSION_MAJOR}
+        VERSION 30
+        SOVERSION 30
         BUILD_RPATH "${OBS_OUTPUT_DIR}/$<CONFIG>/${OBS_LIBRARY_DESTINATION}"
         INSTALL_RPATH "${OBS_LIBRARY_RPATH}"
     )
@@ -107,13 +107,13 @@ function(set_target_properties_obs target)
     endif()
   elseif(target_type STREQUAL MODULE_LIBRARY)
     if(target STREQUAL obs-browser)
-      set_target_properties(${target} PROPERTIES VERSION 0 SOVERSION ${OBS_VERSION_MAJOR})
+      set_target_properties(${target} PROPERTIES VERSION 0 SOVERSION 30)
     else()
       set_target_properties(
         ${target}
         PROPERTIES
           VERSION 0
-          SOVERSION ${OBS_VERSION_MAJOR}
+          SOVERSION 30
           BUILD_RPATH "${OBS_OUTPUT_DIR}/$<CONFIG>/${OBS_LIBRARY_DESTINATION}"
           INSTALL_RPATH "${OBS_MODULE_RPATH}"
       )