Makefile is set to ignore with PHP 7.4, however it compiles/installs and works with PHP 7.4
devel/pecl-propro2 is not marked as IGNORE_WITH_PHP=74, but I believe the error occurred while building www/pecl-http. Please see bug #243911.
(In reply to Muhammad Moinur Rahman from comment #1)
Sorry, looks like I put this on the wrong dependency, it was devel/pecl-raphf2 that also had the Ignore with PHP 7.4.
(In reply to Dean E. Weimer from comment #2)
devel/raphf2 Filed in Bug #244097.