Fix compilation warnings/errors seen with newer versions of gcc compiler.

runtime/third_party/jscre/pcre_compile.cpp

 /* This is JavaScriptCore's variant of the PCRE library. While this library
 started out as a copy of PCRE, many of the features of PCRE have been
 removed. This library now supports only the regular expression features
 required by the JavaScript language specification, and has only the functions
 needed by JavaScriptCore and the rest of WebKit.
 
                  Originally written by Philip Hazel
            Copyright (c) 1997-2006 University of Cambridge
     Copyright (C) 2002, 2004, 2006, 2007 Apple Inc. All rights reserved.
     Copyright (C) 2007 Eric Seidel <eric@webkit.org>
@@ skipping 548 matching lines @@
 {
     int repeat_type, op_type;
     int repeat_min = 0, repeat_max = 0;      /* To please picky compilers */
     int bravalue = 0;
     int reqvary, tempreqvary;
     int c;
     unsigned char* code = *codeptr;
     unsigned char* tempcode;
     bool groupsetfirstbyte = false;
     const UChar* ptr = *ptrptr;
-    const UChar* tempptr;
     unsigned char* previous = NULL;
     unsigned char classbits[32];
     
     bool class_utf8;
     unsigned char* class_utf8data;
     unsigned char utf8_char[6];
     
     /* Initialize no first byte, no required byte. REQ_UNSET means "no char
      matching encountered yet". It gets changed to REQ_NONE if we hit something that
      matches a non-fixed char first char; reqbyte just remains unset if we never
@@ skipping 977 matching lines @@
                     *errorcodeptr = ERR14;
                     goto FAILED;
                 }
                 break;
                 
             /* Check \ for being a real metacharacter; if not, fall through and handle
              it as a data character at the start of a string. Escape items are checked
              for validity in the pre-compiling pass. */
                 
             case '\\':
-                tempptr = ptr;
                 c = checkEscape(&ptr, patternEnd, errorcodeptr, cd.numCapturingBrackets, false);
                 
                 /* Handle metacharacters introduced by \. For ones like \d, the ESC_ values
                  are arranged to be the negation of the corresponding OP_values. For the
                  back references, the values are ESC_REF plus the reference number. Only
                  back references and those types that consume a character may be repeated.
                  We can test for values between ESC_b and ESC_w for the latter; this may
                  have to change if any new ones are ever created. */
                 
                 if (c < 0) {
@@ skipping 1090 matching lines @@
         *numSubpatterns = re->top_bracket;
     return re;
 }
 
 void jsRegExpFree(JSRegExp* re, free_t* free_function)
 {
     (*free_function)(reinterpret_cast<void*>(re));
 }
 
 } }  // namespace dart::jscre