Fix undefined behaviour in string uppercasing and lowercasing

At least on 32-bit, the address computations overflow in running the
test on CI with UBSAN enabled. Fix it by reordering the arithmetic.
Since a part of the expression is already used in the code above the
computation, this should not negatively affect performance.

Closes GH-10936.

Author: ndossche

Zend/zend_operators.c

@@ -2760,7 +2760,7 @@ ZEND_API zend_string* ZEND_FASTCALL zend_string_tolower_ex(zend_string *str, boo
 		if (_mm_movemask_epi8(mingle)) {
 			zend_string *res = zend_string_alloc(length, persistent);
 			memcpy(ZSTR_VAL(res), ZSTR_VAL(str), p - (unsigned char *) ZSTR_VAL(str));
-			unsigned char *q = p + (ZSTR_VAL(res) - ZSTR_VAL(str));
+			unsigned char *q = (unsigned char*) ZSTR_VAL(res) + (p - (unsigned char*) ZSTR_VAL(str));
 
 			/* Lowercase the chunk we already compared. */
 			const __m128i delta = _mm_set1_epi8('a' - 'A');
@@ -2783,7 +2783,7 @@ ZEND_API zend_string* ZEND_FASTCALL zend_string_tolower_ex(zend_string *str, boo
 			zend_string *res = zend_string_alloc(length, persistent);
 			memcpy(ZSTR_VAL(res), ZSTR_VAL(str), p - (unsigned char*) ZSTR_VAL(str));
 
-			unsigned char *q = p + (ZSTR_VAL(res) - ZSTR_VAL(str));
+			unsigned char *q = (unsigned char*) ZSTR_VAL(res) + (p - (unsigned char*) ZSTR_VAL(str));
 			while (p < end) {
 				*q++ = zend_tolower_ascii(*p++);
 			}

ext/standard/string.c

@@ -1373,7 +1373,7 @@ PHPAPI zend_string *php_string_toupper(zend_string *s)
 			if (c != (unsigned char*)ZSTR_VAL(s)) {
 				memcpy(ZSTR_VAL(res), ZSTR_VAL(s), c - (unsigned char*)ZSTR_VAL(s));
 			}
-			r = c + (ZSTR_VAL(res) - ZSTR_VAL(s));
+			r = (unsigned char*) ZSTR_VAL(res) + (c - (unsigned char*) ZSTR_VAL(s));
 			while (c < e) {
 				*r = toupper(*c);
 				r++;
@@ -1438,7 +1438,7 @@ PHPAPI zend_string *php_string_tolower(zend_string *s)
 				if (c != (unsigned char*)ZSTR_VAL(s)) {
 					memcpy(ZSTR_VAL(res), ZSTR_VAL(s), c - (unsigned char*)ZSTR_VAL(s));
 				}
-				r = c + (ZSTR_VAL(res) - ZSTR_VAL(s));
+				r = (unsigned char*) ZSTR_VAL(res) + (c - (unsigned char*) ZSTR_VAL(s));
 				while (c < e) {
 					*r = tolower(*c);
 					r++;