gh-117889: Fix PGO test in test_peg_generator (#117893)

Reuse support.check_cflags_pgo() in test_peg_generator to check for
PGO build.

Log PGO_PROF_USE_FLAG in test.pythoninfo.

Author: vstinner

Lib/test/pythoninfo.py

@@ -513,6 +513,7 @@ def collect_sysconfig(info_add):
         'MACHDEP',
         'MULTIARCH',
         'OPT',
+        'PGO_PROF_USE_FLAG',
         'PY_CFLAGS',
         'PY_CFLAGS_NODIST',
         'PY_CORE_LDFLAGS',

Lib/test/test_peg_generator/test_c_parser.py

@@ -13,9 +13,7 @@
 from test.support import os_helper, import_helper
 from test.support.script_helper import assert_python_ok
 
-_py_cflags_nodist = sysconfig.get_config_var("PY_CFLAGS_NODIST")
-_pgo_flag = sysconfig.get_config_var("PGO_PROF_USE_FLAG")
-if _pgo_flag and _py_cflags_nodist and _pgo_flag in _py_cflags_nodist:
+if support.check_cflags_pgo():
     raise unittest.SkipTest("peg_generator test disabled under PGO build")
 
 test_tools.skip_if_missing("peg_generator")