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

Calculating dependencies ... done!
Dependency resolution took 1.51 s (backtrack: 0/20).

[ebuild  N     ] perl-core/Scalar-List-Utils-1.630.0::gentoo  PERL_FEATURES="ithreads (-debug) -quadmath" 174 KiB
[blocks B      ] <perl-core/Scalar-List-Utils-1.680.100_rc ("<perl-core/Scalar-List-Utils-1.680.100_rc" is soft blocking virtual/perl-Scalar-List-Utils-1.680.100_rc)

Total: 1 package (1 new), Size of downloads: 174 KiB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (perl-core/Scalar-List-Utils-1.630.0:0/0::gentoo, ebuild scheduled for merge) pulled in by
    =perl-core/Scalar-List-Utils-1.630.0

  (virtual/perl-Scalar-List-Utils-1.680.100_rc:0/0::gentoo, installed) pulled in by
    =virtual/perl-Scalar-List-Utils-1.680.100_rc required by (dev-perl/DBD-SQLite-1.760.0:0/0::gentoo, installed) USE="-system-sqlite -test" PERL_FEATURES="ithreads (-debug) -quadmath"
    =virtual/perl-Scalar-List-Utils-1.680.100_rc required by (dev-perl/DBI-1.647.0:0/0::gentoo, installed) USE="-examples -test" PERL_FEATURES="ithreads (-debug) -quadmath"
    virtual/perl-Scalar-List-Utils required by (dev-perl/DBI-1.647.0:0/0::gentoo, installed) USE="-examples -test" PERL_FEATURES="ithreads (-debug) -quadmath"
    virtual/perl-Scalar-List-Utils required by (dev-perl/DBD-SQLite-1.760.0:0/0::gentoo, installed) USE="-system-sqlite -test" PERL_FEATURES="ithreads (-debug) -quadmath"
    =virtual/perl-Scalar-List-Utils-1.680.100_rc required by (dev-perl/Params-Util-1.102.0:0/0::gentoo, installed) USE="-test" PERL_FEATURES="ithreads (-debug) -quadmath"
    >=virtual/perl-Scalar-List-Utils-1.180.0 required by (dev-perl/Params-Util-1.102.0:0/0::gentoo, installed) USE="-test" PERL_FEATURES="ithreads (-debug) -quadmath"
    =virtual/perl-Scalar-List-Utils-1.680.100_rc required by (dev-perl/Config-AutoConf-0.320.0:0/0::gentoo, installed) USE="-test" PERL_FEATURES="ithreads (-debug) -quadmath"
    >=virtual/perl-Scalar-List-Utils-1.180.0 required by (dev-perl/Config-AutoConf-0.320.0:0/0::gentoo, installed) USE="-test" PERL_FEATURES="ithreads (-debug) -quadmath"


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages