p5-compress-stream-zstd uses wrong compiler

[jmroot (Joshua Root)]

​https://build.macports.org/builders/ports-10.6_x86_64-builder/builds/102164/steps/install-port/logs/stdio

The first compiler command run is

cc -DZSTD_MULTITHREAD -DZSTD_LEGACY_MULTITHREADED_API -O3 -fPIC -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow -Wstrict-aliasing=1 -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wundef -Wpointer-arith -Wvla -Wformat=2 -Winit-self -Wfloat-equal -Wwrite-strings -Wredundant-decls -Wmissing-prototypes -Wc++-compat  -I. -I./common -DXXH_NAMESPACE=ZSTD_ -I./legacy -DZSTD_LEGACY_SUPPORT=5  -c -o common/debug.o common/debug.c

Not sure where it's getting cc; that's not even the compiler baked into perl. Later commands do appear to be using the right compiler.