illumos gate

Build errors when warnings are enabled:

    ../env.c: In function 'efi_print_var':
    ../env.c:690:38: error: pointer targets in passing argument 2 of 'efi_print_global' differ in signedness [-Werror=pointer-sign]
        rv = efi_print_global(varnamearg, data, datasz);
                                          ^~~~
    ../env.c:480:1: note: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'char *'
     efi_print_global(const CHAR16 *varnamearg, uint8_t *data, UINTN datasz)
     ^~~~~~~~~~~~~~~~
    ../env.c:692:39: error: pointer targets in passing argument 2 of 'efi_print_illumos' differ in signedness [-Werror=pointer-sign]
        rv = efi_print_illumos(varnamearg, data, datasz);
                                           ^~~~
    ../env.c:455:1: note: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'char *'
     efi_print_illumos(const CHAR16 *varnamearg, uint8_t *data, UINTN datasz)
     ^~~~~~~~~~~~~~~~~
    ../env.c:695:40: error: pointer targets in passing argument 2 of 'efi_print_mem_type' differ in signedness [-Werror=pointer-sign]
        rv = efi_print_mem_type(varnamearg, data, datasz);
                                            ^~~~
    ../env.c:430:1: note: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'char *'
     efi_print_mem_type(const CHAR16 *varnamearg, uint8_t *data, UINTN datasz)
     ^~~~~~~~~~~~~~~~~~
    ../env.c:698:41: error: pointer targets in passing argument 2 of 'efi_print_shell_str' differ in signedness [-Werror=pointer-sign]
        rv = efi_print_shell_str(varnamearg, data, datasz);
                                             ^~~~
    ../env.c:377:1: note: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'char *'
     efi_print_shell_str(const CHAR16 *varnamearg, uint8_t *data, UINTN datasz)
     ^~~~~~~~~~~~~~~~~~~
    ../env.c:706:31: error: pointer targets in passing argument 1 of 'efi_print_other_value' differ in signedness [-Werror=pointer-sign]
        rv = efi_print_other_value(data, datasz);
                                   ^~~~
    ../env.c:330:1: note: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'char *'
     efi_print_other_value(uint8_t *data, UINTN datasz)
     ^~~~~~~~~~~~~~~~~~~~~