In #664942 there was a dependency on app-crypt/mit-krb5 due to a header file, but now it wants to link to the actual library:
x86_64-pc-linux-gnu-gcc -m32 -L. -march=native -O2 -pipe -g -Wall -Wl,-O1 -Wl,--as-needed -o key.dns_resolver \
key.dns_resolver.o dns.afsdb.o -lkrb5 -lcom_err -lkeyutils -lresolv
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lkrb5
collect2: error: ld returned 1 exit status
make: *** [Makefile:156: key.dns_resolver] Error 1
And just trying to install app-crypt/mit-krb5 does not easily fix it, because that package depends on keyutils and tries to build it first.
Well, for me that looks like a normal circular dependency you sometimes have to deal with: Install app-crypt/mit-krb5[-keyutils] first, then emerge sys-apps/keyutils and finally re-emerge app-crypt/mit-krb5 with USE=keyutils again if you need that.