cmake: Fix build directory exclusion

The regex was incorrectly excluding any file with build in the name. The
intent was to exclude any build directories, so we should be able to
restrict this.

cmake/linux/cpackconfig.cmake

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