argyll @2.2.1_1 fails to compile on macOS 12.1

[dwightkelly (Dwight Kelly)]

The error below occur while installing argyll @2.2.1_1 on macOS 12.1 Apple clang version 13.0.0 (clang-1300.0.27.3) Target: x86_64-apple-darwin21.2.0 Thread model: posix

:info:build execunix.c:234:6: error: implicit declaration of function 'execvp' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
:info:build             execvp( argv[0], argv );
:info:build             ^
:info:build execunix.c:235:6: error: implicitly declaring library function '_exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
:info:build             _exit(127);
:info:build             ^
:info:build execunix.c:235:6: note: include the header <unistd.h> or explicitly provide a declaration for '_exit'