[contrib] validate_failures.py: Don't consider summary line in wrong place

[contrib] validate_failures.py: Don't consider summary line in wrong place

When parsing a summary or manifest file, if we're not either after a tool
line (e.g. "=== gdb tests ===") or before a summary line (e.g.,
"=== gdb Summary ===") then the current line can't be a valid result line
so ignore it.

This addresses a problem we're seeing when running the GDB testsuite in
our CI environment where it produces a valid summary file, but then after
the "=== gdb Summary ===" section it outputs a series of Tcl errors that
match _VALID_TEST_RESULTS_REX and thus confuse the parsing logic:

05: 14:32 .sum file seems to be broken: tool="None", exp="None", summary_line="ERROR: -------------------------------------------"
05: 14:32 Traceback (most recent call last):
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 706, in <module>
05: 14:32     retval = Main(sys.argv)
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 697, in Main
05: 14:32     retval = CheckExpectedResults()
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 572, in CheckExpectedResults
05: 14:32     actual = GetResults(sum_files)
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 447, in GetResults
05: 14:32     build_results.update(ParseSummary(sum_fname))
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 389, in ParseSummary
05: 14:32     result = result_set.MakeTestResult(line, ordinal)
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 236, in MakeTestResult
05: 14:32     return TestResult(summary_line, ordinal,
05: 14:32   File "/path/to/gcc/contrib/testsuite-management/validate_failures.py", line 148, in __init__
05: 14:32     raise

contrib/ChangeLog:

	* testsuite-management/validate_failures.py (IsInterestingResult):
	Add result_set argument and use it.  Adjust callers.