These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.08 s (backtrack: 0/20).

[ebuild  N     ] net-libs/mbedtls-2.28.10:0/7.14.1::gentoo  USE="havege threads -cmac -doc -programs -static-libs -test -zlib" CPU_FLAGS_X86="sse2" 3408 KiB
[ebuild  N     ] net-libs/zeromq-4.3.5-r1:0/5::gentoo  USE="libbsd sodium -doc -drafts -static-libs -test -unwind" 2471 KiB
[ebuild  N     ] www-servers/mongrel2-1.11.0-r3::gentoo  1036 KiB

Total: 3 packages (3 new), Size of downloads: 6915 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by www-servers/mongrel2-1.11.0-r3::gentoo
# required by =www-servers/mongrel2-1.11.0-r3 (argument)
>=net-libs/mbedtls-2.28.10:0 havege