Change gcc version check in test runner to a numeric comparison (GH-4359)

The string comparison was reporting '11' < '4' (so OpenMP tests were being skipped on GCC 11)

runtests.py

@@ -362,7 +362,9 @@ def get_openmp_compiler_flags(language):
     COMPILER_HAS_INT128 = getattr(sys, 'maxsize', getattr(sys, 'maxint', 0)) > 2**60
 
     compiler_version = gcc_version.group(1)
-    if compiler_version and compiler_version.split('.') >= ['4', '2']:
+    if compiler_version:
+        compiler_version = [int(num) for num in compiler_version.split('.')]
+        if compiler_version >= [4, 2]:
             return '-fopenmp', '-fopenmp'
 
 try: