patch 8.0.0452: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case.
diff --git a/src/diff.c b/src/diff.c
index 8c70e0c..246c4e0 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1667,7 +1667,7 @@
     p2 = s2;
     while (*p1 != NUL && *p2 != NUL)
     {
-	if (vim_iswhite(*p1) && vim_iswhite(*p2))
+	if (VIM_ISWHITE(*p1) && VIM_ISWHITE(*p2))
 	{
 	    p1 = skipwhite(p1);
 	    p2 = skipwhite(p2);
@@ -1994,8 +1994,8 @@
 	    while (line_org[si_org] != NUL)
 	    {
 		if ((diff_flags & DIFF_IWHITE)
-			&& vim_iswhite(line_org[si_org])
-			&& vim_iswhite(line_new[si_new]))
+			&& VIM_ISWHITE(line_org[si_org])
+			&& VIM_ISWHITE(line_new[si_new]))
 		{
 		    si_org = (int)(skipwhite(line_org + si_org) - line_org);
 		    si_new = (int)(skipwhite(line_new + si_new) - line_new);
@@ -2029,14 +2029,14 @@
 						&& ei_org >= 0 && ei_new >= 0)
 		{
 		    if ((diff_flags & DIFF_IWHITE)
-			    && vim_iswhite(line_org[ei_org])
-			    && vim_iswhite(line_new[ei_new]))
+			    && VIM_ISWHITE(line_org[ei_org])
+			    && VIM_ISWHITE(line_new[ei_new]))
 		    {
 			while (ei_org >= *startp
-					     && vim_iswhite(line_org[ei_org]))
+					     && VIM_ISWHITE(line_org[ei_org]))
 			    --ei_org;
 			while (ei_new >= si_new
-					     && vim_iswhite(line_new[ei_new]))
+					     && VIM_ISWHITE(line_new[ei_new]))
 			    --ei_new;
 		    }
 		    else
@@ -2202,7 +2202,7 @@
     {
 	/* Buffer number or pattern given.  Ignore trailing white space. */
 	p = eap->arg + STRLEN(eap->arg);
-	while (p > eap->arg && vim_iswhite(p[-1]))
+	while (p > eap->arg && VIM_ISWHITE(p[-1]))
 	    --p;
 	for (i = 0; vim_isdigit(eap->arg[i]) && eap->arg + i < p; ++i)
 	    ;