illumos gate

Issue found by gcc 8 build:

    ../common/misc/mime.c: In function 'mimehead':
    ../common/misc/mime.c:744:37: error: cast between incompatible function types from 'int (*)(const char *, const char *, char **)' to 'int (*)(const char *, const char *)' [-Werror=cast-function-type]
       if ((p = strsearch(tab, num, siz, (Strcmp_f)mimecmp, s, &e)) && *e == ':')
                                         ^
    ../common/misc/mime.c:753:40: error: cast between incompatible function types from 'int (*)(const char *, const char *, char **)' to 'int (*)(const char *, const char *)' [-Werror=cast-function-type]
              (p = strsearch(tab, num, siz, (Strcmp_f)mimecmp, pp.name.data, &e)) &&
                                            ^
    ../common/misc/glob.c: In function '_ast_glob':
    ../common/misc/glob.c:630:22: error: cast between incompatible function types from 'int (*)(DIR *)' {aka 'int (*)(struct <anonymous> *)'} to 'void (*)(void *)' [-Werror=cast-function-type]
        gp->gl_closedir = (GL_closedir_f)closedir;
                          ^
    ../common/string/strsearch.c: In function '_ast_strsearch':
    ../common/string/strsearch.c:50:25: error: cast between incompatible function types from 'Strcmp_f' {aka 'int (*)(const char *, const char *)'} to 'int (*)(const char *, const char *, void *)' [-Werror=cast-function-type]
       if (!(v = context ? (*(Strcmp_context_f)comparf)(name, *((char**)mid), context) : (*comparf)(name, *((char**)mid))))
                             ^
    cc1: all warnings being treated as errors

Add proper wrapper function and cast over uintptr_t.