MT#60408 Don't use register storage class for READ_NUMBER

Don't store `fin` variable in a processor register
but store as usually in memory.

Resolves:

parse_100rel.cpp: In function 'bool parse_rseq(unsigned int*, const char*, int)':
parse_100rel.cpp:19:19: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   19 |     register bool fin; \
      |                   ^~~
parse_100rel.cpp:55:3: note: in expansion of macro 'READ_NUMBER'
   55 |   READ_NUMBER(rseq, pos, end);
      |   ^~~~~~~~~~~
parse_100rel.cpp: In function 'bool parse_rack(sip_rack*, const char*, int)':
parse_100rel.cpp:19:19: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   19 |     register bool fin; \
      |                   ^~~
parse_100rel.cpp:84:3: note: in expansion of macro 'READ_NUMBER'
   84 |   READ_NUMBER(rseq, pos, end);
      |   ^~~~~~~~~~~
parse_100rel.cpp:19:19: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   19 |     register bool fin; \
      |                   ^~~
parse_100rel.cpp:91:3: note: in expansion of macro 'READ_NUMBER'
   91 |   READ_NUMBER(cseq, pos, end);
      |   ^~~~~~~~~~~

Change-Id: I9030a5ac8b7ebb0dd1b932296f73a7987639fc26

core/sip/parse_100rel.cpp

@@ -16,7 +16,7 @@
 
 #define READ_NUMBER(_no, _c_, _end_) \
   do { \
-    register bool fin; \
+    bool fin; \
     (_no) = 0; \
     for (fin = false; !fin && (_c_) < (_end_); ) { \
       switch (*(_c_)) { \