Bootstrapped plx's inline cpanm does not inherit PERL_CPANM_HOME environment variable.

[NicholasBHubbard]

plx version: 0.902003

Reproduction steps:

$ echo $0
/bin/bash

$ cd $HOME

$ mkdir -p foo/bin

$ cd foo

foo$ wget https://raw.githubusercontent.com/shadowcat-mst/plx/master/bin/plx-packed -O bin/plx
--2022-03-27 18:54:31--  https://raw.githubusercontent.com/shadowcat-mst/plx/master/bin/plx-packed
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.108.133, 185.199.109.133, 185.199.110.133, ...
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.108.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 398007 (389K) [text/plain]
Saving to: ‘bin/plx’

bin/plx             100%[===================>] 388.68K  1.88MB/s    in 0.2s    

2022-03-27 18:54:31 (1.88 MB/s) - ‘bin/plx’ saved [398007/398007]
foo$ chmod 555 bin/plx

foo$ bin/plx --init /bin/perl

foo$ export PERL_CPANM_HOME=$HOME/foo/.cpanm

foo$ bin/plx --cpanm -L local -i Regexp::Debugger
Running packed cpanm
--> Working on Regexp::Debugger
Fetching http://www.cpan.org/authors/id/D/DC/DCONWAY/Regexp-Debugger-0.002006.tar.gz ... OK
Configuring Regexp-Debugger-0.002006 ... OK
Building and testing Regexp-Debugger-0.002006 ... OK
Successfully installed Regexp-Debugger-0.002006
1 distribution installed

foo$ ls -a | grep cpanm

foo$ ls -a $HOME | grep cpanm
.cpanm

This output shows that the exported PERL_CPANM_HOME variable is ignored and cpanm uses the default directory $HOME/.cpanm as the cpanm home.