current ebuild sets $BUILD_FLAGS in src_compile() to include -D HTTP_BOOT_ENABLE -D TLS_ENABLE for building with HTTP{S] support enabled. however, these defines have been (long) renamed to NETWORK_HTTP_BOOT_ENABLE and NETWORK_TLS_ENABLE with https://github.com/tianocore/edk2/commit/631195044ff0 thus the current builds of sys-firmware/edk2-ovmf (and the derived sys-firmware/edk2-ovmf-bin) lack HTTP[S] boot support. this got also updated in the README (https://github.com/tianocore/edk2/commit/1631bb26ae991e530d3c96fe3161ea15144b358e)