macOS ARM bottle has implicit zstd dependency

[roscopeco]

Problem

The gcc-cross-m68k@13 macOS bottle for M-series (at least, this could easily affect others) has an undeclared dependency on zstd that causes the bottle to install, but then the installed binaries to be inoperable.

Workaround

brew install zstd

Fix

Declare a dependency on zstd in the formula

m68k-elf-gcc -c -std=c11 -ffreestanding -ffunction-sections -fdata-sections -nostartfiles -Wall -Wpedantic -Werror -mcpu=68010 -march=68010 -mtune=68010  -DROSCO_M68K_SYSLIBS -Isrc/cstdlib/include -DBUILD_ROSCOM68K_CSTDLIB_LIB -Isrc/sdfat/include -DBUILD_ROSCOM68K_SDFAT_LIB -DFATFS_USE_CUSTOM_OPTS_FILE -Wno-unused-function -Isrc/machine/include -DBUILD_ROSCOM68K_MACHINE_LIB -Isrc/easy68k/include -DBUILD_ROSCOM68K_EASY68K_LIB -Isrc/debug_stub/include -DBUILD_ROSCOM68K_DEBUG_STUB_LIB -DBUILD_ROSCOM68K_START_SERIAL_LIB -Isrc/vterm/include -DBUILD_ROSCOM68K_VTERM_LIB -Isrc/libm/include -DBUILD_ROSCOM68K_M_LIB -Wno-error=maybe-uninitialized -Isrc/sst_flash/include -DBUILD_ROSCOM68K_SST_FLASH_LIB -Isrc/shmall/include -DBUILD_ROSCOM68K_HEAP_LIB -Isrc/gdb/include -DBUILD_ROSCOM68K_GDB_LIB -Isrc/printf/include -DBUILD_ROSCOM68K_PRINTF_LIB -DPRINTF_INCLUDE_CONFIG_H -g -O2 -o src/cstdlib/ctype.o src/cstdlib/ctype.c
dyld[43548]: Library not loaded: /opt/homebrew/opt/zstd/lib/libzstd.1.dylib
  Referenced from: <91038065-B08A-3600-B521-8F54FFA637D9> /opt/homebrew/Cellar/gcc-cross-m68k@13/13.3.0.reinstall/libexec/gcc/m68k-elf/13.3.0/cc1
  Reason: tried: '/opt/homebrew/opt/zstd/lib/libzstd.1.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/opt/homebrew/opt/zstd/lib/libzstd.1.dylib' (no such file), '/opt/homebrew/opt/zstd/lib/libzstd.1.dylib' (no such file)
m68k-elf-gcc: internal compiler error: Abort trap: 6 signal terminated program cc1
Please submit a full bug report, with preprocessed source (by using -freport-bug).
See https://gcc.gnu.org/bugs/ for instructions.
make: *** [src/cstdlib/ctype.o] Error 4