Refactor to avoid sanitize warnings when accessing the variable size ovector in

the backtracking frame. Fixes oss-fuzz issue 1465. Also make -bigstack in 
RunTest allocate a 64Mb stack for use with clang sanitizing.

ChangeLog

@@ -39,6 +39,9 @@ bugs were never in fully released code, but are noted here for the record.
   (f) Refactor some code in do_callout() to avoid picky compiler warnings about 
       negative indices. Fixes oss-fuzz issue 1454.
       
+  (g) Similarly refactor the way the variable length ovector is addressed for
+      similar reasons. Fixes oss-fuzz issue 1465.
+ 
       
 2. Now that pcre2_match() no longer uses recursive function calls (see above),
 the "match limit recursion" value seems misnamed. It still exists, and limits 
@@ -160,6 +163,9 @@ tests to improve coverage.
 31. If more than one of "push", "pushcopy", or "pushtablescopy" were set in 
 pcre2test, a crash could occur.
 
+32. Make -bigstack in RunTest allocate a 64Mb stack (instead of 16 MB) so that 
+all the tests can run with clang's sanitizing options.
+
 
 
 Version 10.23 14-February-2017

RunTest

@@ -321,7 +321,7 @@ fi
 
 $sim ./pcre2test -S 1 /dev/null /dev/null
 if [ $? -eq 0 -a "$bigstack" != "" ] ; then
-  setstack="-S 16"
+  setstack="-S 64"
 else
   setstack=""
 fi

src/pcre2_match.c

@@ -182,9 +182,15 @@ of use and undefined afterwards. */
 #define Foffset_top        F->offset_top
 #define Foccu              F->occu
 #define Fop                F->op
-#define Fovector           F->ovector
 #define Freturn_id         F->return_id
 
+/* We need a cast for this one because F->ovector is a vector of size 2, at the 
+end of the backtrack frame, but when there are capturing parentheses the space 
+allocated is bigger so we want to be able to address more elements. Without the 
+case, -fsanitize=undefined grumbles at this. */
+
+#define Fovector           ((PCRE2_SIZE *)(F->ovector))
+
 
 #ifdef DEBUG_FRAMES_DISPLAY
 /*************************************************