Adding an option to control the environment variables that are being passed into the child processes

[AnirudhKanaparthy]

// Options for nob_cmd_run_opt() function.
typedef struct {
    // Run the command asynchronously appending its Nob_Proc to the provided Nob_Procs array
    Nob_Procs *async;
    
    char *const *env; // <-- New Field!

    // Maximum processes allowed in the .async list. Zero implies nob_nprocs().
    size_t max_procs;
    // Do not reset the command after execution.
    bool dont_reset;
    // Redirect stdin to file
    const char *stdin_path;
    // Redirect stdout to file
    const char *stdout_path;
    // Redirect stderr to file
    const char *stderr_path;
} Nob_Cmd_Opt;

This is useful for when you want to run executables which depend on certain environment variables to be set like in the case of some Qt applications.

char *const *custom_env = clone_env(environ);
env_set(custom_env, "QT_QPA_PLATFORM_PLUGIN_PATH", "/path/to/your/platform/plugins");

Cmd cmd = {0};
cmd_append(&cmd, "./qtapp");
cmd_run(&cmd, .env=custom_env);

It can be even used to modify the PATH variable.

const char* path = env_get(custom_env, "PATH");
const char new_loc[] = "/custom/path";

size_t new_path_len = strlen(path) + strlen(new_loc) + sizeof(":");
char* new_path = (char*)calloc(new_path_len, sizeof(char));
snprintf(new_path, new_path_len, "%s:%s", new_loc, path);

env_set(custom_env, "PATH", new_path);

Cmd cmd = {0};
cmd_append(&cmd, "./some_bs_cross_compile_script.sh");
cmd_run(&cmd, .env=custom_env);