cmake HAVE_SIGTHREADMASK examples

arkdb/inception configure.cmake :468

CHECK_FUNCTION_EXISTS (sigthreadmask HAVE_SIGTHREADMASK)

alibaba/AliSQL configure.cmake :575

CHECK_FUNCTION_EXISTS (sigthreadmask HAVE_SIGTHREADMASK)

Tokutek/mysql-5.5 configure.cmake :408

CHECK_FUNCTION_EXISTS (sigthreadmask HAVE_SIGTHREADMASK)