I removed perlbrew and made certain I had no offensive environment variables before reinstalling it.

After reinstallation, I loaded up cpanm and tried first an XS module I have historically had no issues with (JSON::XS); then List::MoreUtils...

gcp4al16:rg8239$ which cpanm
~/perl5/perlbrew/bin/cpanm
gcp4al16:rg8239$ cpanm JSON::XS
--> Working on JSON::XS
Fetching http://www.cpan.org/authors/id/M/ML/MLEHMANN/JSON-XS-4.02.tar
+.gz ... OK
==> Found dependencies: Canary::Stability
--> Working on Canary::Stability
Fetching http://www.cpan.org/authors/id/M/ML/MLEHMANN/Canary-Stability
+-2013.tar.gz ... OK
Configuring Canary-Stability-2013 ... OK
Building and testing Canary-Stability-2013 ... OK
Successfully installed Canary-Stability-2013
Configuring JSON-XS-4.02 ... OK
==> Found dependencies: common::sense, Types::Serialiser
--> Working on common::sense
Fetching http://www.cpan.org/authors/id/M/ML/MLEHMANN/common-sense-3.7
+5.tar.gz ... OK
Configuring common-sense-3.75 ... OK
Building and testing common-sense-3.75 ... OK
Successfully installed common-sense-3.75
--> Working on Types::Serialiser
Fetching http://www.cpan.org/authors/id/M/ML/MLEHMANN/Types-Serialiser
+-1.0.tar.gz ... OK
Configuring Types-Serialiser-1.0 ... OK
Building and testing Types-Serialiser-1.0 ... OK
Successfully installed Types-Serialiser-1.0
Building and testing JSON-XS-4.02 ... OK
Successfully installed JSON-XS-4.02
4 distributions installed
[download]

gcp4al16:rg8239$ cpanm List::MoreUtils
--> Working on List::MoreUtils
Fetching http://www.cpan.org/authors/id/R/RE/REHSACK/List-MoreUtils-0.
+428.tar.gz ... OK
Configuring List-MoreUtils-0.428 ... OK
==> Found dependencies: List::MoreUtils::XS, Test::LeakTrace, Exporter
+::Tiny
--> Working on List::MoreUtils::XS
Fetching http://www.cpan.org/authors/id/R/RE/REHSACK/List-MoreUtils-XS
+-0.428.tar.gz ... OK
Configuring List-MoreUtils-XS-0.428 ... OK
Building and testing List-MoreUtils-XS-0.428 ... FAIL
! Installing List::MoreUtils::XS failed. See /home/rg8239/.cpanm/work/
+1597187453.8905/build.log for details. Retry with --force to f
orce install it.
--> Working on Test::LeakTrace
Fetching http://www.cpan.org/authors/id/L/LE/LEEJO/Test-LeakTrace-0.16
+.tar.gz ... OK
Configuring Test-LeakTrace-0.16 ... OK
Building and testing Test-LeakTrace-0.16 ... OK
Successfully installed Test-LeakTrace-0.16
--> Working on Exporter::Tiny
Fetching http://www.cpan.org/authors/id/T/TO/TOBYINK/Exporter-Tiny-1.0
+02002.tar.gz ... OK
Configuring Exporter-Tiny-1.002002 ... OK
Building and testing Exporter-Tiny-1.002002 ... OK
Successfully installed Exporter-Tiny-1.002002
! Installing the dependencies failed: Module 'List::MoreUtils::XS' is 
+not installed
! Bailing out the installation for List-MoreUtils-0.428.
2 distributions installed
[download]

Obviously, still no luck