cpukit/libcsupport: Address -Wsign-compare warnings

This warning occurs when comparing a signed variable to an unsigned one.
This addresses warnings that only occurred on 64-bit targets.  For the
ones which only appeared on 64-bit targets, the cause was frequently
a mismatch when comparing a combination off_t, ssize_t, and int.

cpukit/libcsupport/src/pwdgrp.c

@@ -134,7 +134,7 @@ scanInt(FILE *fp, int *val)
   int i = 0;
   int limit = INT_MAX;
   int sign = 0;
-  int d;
+  unsigned int d;
 
   for (;;) {
     c = getc(fp);