Disable peg generator tests when building with PGO

Otherwise, when running the testsuite, test_peg_generator tries to compile C
code using the optimized flags and fails because it cannot find the profile
data.

https://bugs.python.org/issue42207

Author: serge-sans-paille

Lib/test/test_peg_generator/test_c_parser.py

@@ -1,3 +1,4 @@
+import sysconfig
 import textwrap
 import unittest
 from distutils.tests.support import TempdirManager
@@ -8,6 +9,10 @@
 from test.support import os_helper
 from test.support.script_helper import assert_python_ok
 
+_pyflags_nodist = sysconfig.get_config_var('PY_CFLAGS_NODIST') or ()
+if sysconfig.get_config_var('PGO_PROF_USE_FLAG') in _pyflags_nodist:
+    raise unittest.SkipTest("peg_generator test disabled when building with PGO")
+
 test_tools.skip_if_missing("peg_generator")
 with test_tools.imports_under_tool("peg_generator"):
     from pegen.grammar_parser import GeneratedParser as GrammarParser