use REQUIRED in find_package(GMM) instead of fatal error

CMakeLists.txt

@@ -60,14 +60,13 @@ else()
 endif ()
 
 
-find_package (GMM)
+find_package (GMM REQUIRED)
 if (GMM_FOUND)
   set (COMISO_GMM_CONFIG_FILE_SETTINGS "#define COMISO_GMM_AVAILABLE 1" )
   list( APPEND COMISO_INCLUDE_DIRECTORIES ${GMM_INCLUDE_DIR} )
   list (APPEND NEED_LAPACK "GMM")
 else()
   set (COMISO_GMM_CONFIG_FILE_SETTINGS "#define COMISO_GMM_AVAILABLE 0" )
-  message (FATAL_ERROR "GMM not found!")
 endif ()
 
 set(TMP_CMAKE_FIND_LIBRARY_PREFIXES "${CMAKE_FIND_LIBRARY_PREFIXES}")