bpo-43244: Fix test_peg_generators on Windows (GH-24913)

Don't redefine Py_DebugFlag, it's already defined in pydebug.h which
is included by Python.h

Author: vstinner

Parser/parser.c

@@ -2,10 +2,9 @@
 #include "pegen.h"
 
 #if defined(Py_DEBUG) && defined(Py_BUILD_CORE)
-extern int Py_DebugFlag;
-#define D(x) if (Py_DebugFlag) x;
+#  define D(x) if (Py_DebugFlag) x;
 #else
-#define D(x)
+#  define D(x)
 #endif
 static const int n_keyword_lists = 9;
 static KeywordToken *reserved_keywords[] = {

Tools/peg_generator/pegen/c_generator.py

@@ -31,10 +31,9 @@
 #include "pegen.h"
 
 #if defined(Py_DEBUG) && defined(Py_BUILD_CORE)
-extern int Py_DebugFlag;
-#define D(x) if (Py_DebugFlag) x;
+#  define D(x) if (Py_DebugFlag) x;
 #else
-#define D(x)
+#  define D(x)
 #endif
 
 """