This package fails to compile on a stable system. Attached relevant logs and emerge --info
Created attachment 691368 [details] emerge_info emerge --info
Created attachment 691371 [details] x11-drivers:xf86-video-intel-2.99.917_p20201215:20210314-113918.log build log
Created attachment 691374 [details] autoconf.out relevant log
Strange. It looks like x11-misc/util-macros is missing from your system. Can you confirm that it's not installed? But it's automatically added to BDEPEND by xorg-3.eclass when XORG_EAUTORECONF=yes is set, which it is...
Libtool was also broken so I started 'emerge -e world' to see if something will improve. Well it works now, I don't know what exactly was broken but it has not been catched by our tools.