Enhance `mkstemps` detection on linux with glibc version sniffing.

According to https://sourceware.org/git/?p=glibc.git;a=blob;f=NEWS;h=63be362731c0a3c7021485284a7abbefb86ab228;hb=HEAD , `mkstemps` was added to glibc in version 2.11 and as such may not be available on all glibc-based platforms. RHEL5 is still based on glibc 2.5, for instance.