Replaced `NO_IO_POPEN` with `MRB_NO_IO_POPEN`
ref. commit
@@ -339,7 +339,7 @@ io_alloc(mrb_state *mrb)
#define NOFILE 64
#endif
-#ifdef NO_IO_POPEN
+#ifdef MRB_NO_IO_POPEN
# define io_s_popen mrb_notimplement_m
#else
static int
@@ -770,7 +770,7 @@ fptr_finalize(mrb_state *mrb, struct mrb_io *fptr, int quiet)
fptr->fd2 = -1;
}
-#ifndef NO_IO_POPEN
+#ifndef MRB_NO_IO_POPEN
if (fptr->pid != 0) {
#if !defined(_WIN32) && !defined(_WIN64)
pid_t pid;
