cmake: Fix build directory exclusion for real

Upon further review, the build directory is never set to build_$arch.
Currently, our CMake Presets on Ubuntu only use build_ubuntu. However,
we can attempt to be flexible here and simply exclude the build
directory configured in CMake.

cmake/linux/cpackconfig.cmake

@@ -16,7 +16,7 @@ endif()
 
 set(CPACK_SOURCE_PACKAGE_FILE_NAME "obs-studio-${CPACK_PACKAGE_VERSION}-sources")
 set(CPACK_SOURCE_GENERATOR "TGZ")
-set(CPACK_SOURCE_IGNORE_FILES "/.git" "/build_${CMAKE_SYSTEM_PROCESSOR}" "/.ccache" "/.deps")
+set(CPACK_SOURCE_IGNORE_FILES "/.git" "${CMAKE_BINARY_DIR}" "/.ccache" "/.deps")
 set(CPACK_ARCHIVE_THREADS 0)
 
 if(OS_LINUX)