*: optimize most of isXXXXX() macros

   text    data     bss     dec     hex filename
 824164     453    6812  831429   cafc5 busybox_old
 823730     453    6812  830995   cae13 busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/fdisk.c b/util-linux/fdisk.c
index 1bb3a9d..6a194fd 100644
--- a/util-linux/fdisk.c
+++ b/util-linux/fdisk.c
@@ -460,7 +460,7 @@
 		line_buffer[--sz] = '\0';
 
 	line_ptr = line_buffer;
-	while (*line_ptr && !isgraph(*line_ptr))
+	while (*line_ptr != '\0' && (unsigned char)*line_ptr <= ' ')
 		line_ptr++;
 	return *line_ptr;
 }