PR demangler/80513 check for overflows and invalid characters in thunks

PR demangler/80513 check for overflows and invalid characters in thunks

	PR demangler/80513
	* cp-demangle.c (d_number): Check for overflow.
	* cplus-dem.c (consume_count): Fix overflow check.
	(gnu_special): Check for underscore after thunk delta.
	* testsuite/demangle-expected: Add tests for overflows and invalid
	characters in thunks.

From-SVN: r247300