libbb: stop using bb_strtod for now

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/sleep.c b/coreutils/sleep.c
index de18dd0..b16d03c 100644
--- a/coreutils/sleep.c
+++ b/coreutils/sleep.c
@@ -54,11 +54,13 @@
 		char *arg = *argv;
 		if (strchr(arg, '.')) {
 			double d;
+			char *pp;
 			int len = strspn(arg, "0123456789.");
 			char sv = arg[len];
 			arg[len] = '\0';
-			d = bb_strtod(arg, NULL);
-			if (errno)
+			errno = 0;
+			d = strtod(arg, &pp);
+			if (errno || *pp)
 				bb_show_usage();
 			arg[len] = sv;
 			len--;