[committed][gdb/symtab] Make per_cu->m_lang atomic

[Tom Tromey]

>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes:

Tom>    /* The language of this CU.  */
Tom> -  packed<language, LANGUAGE_BYTES> m_lang = language_unknown;
Tom> +  std::atomic<packed<language, LANGUAGE_BYTES>> m_lang {language_unknown};
 
These changes seem fine to me but I wonder whether they have a
performance impact.

Tom