(I'm not sure if it's using CC or GCC). I'm stumped. Any advice appreciated.

forget about perlbrew :) try perlall

OR, try it yourself :) given the diagnostic message you got is I'm giving up; maybe you can try again with a different compiler? so run configure yourself with prefix and specify your compiler as gcc

sh configure -Dcc=gcc -Dprefix=~/p5180
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