GH-99104: Update headers for bytecodes.c and generate_cases.py (#99112)

Also tweak the labels near the end of bytecodes.c.

Author: gvanrossum

Python/bytecodes.c

@@ -1,3 +1,11 @@
+// This file contains instruction definitions.
+// It is read by Tools/cases_generator/generate_cases.py
+// to generate Python/generated_cases.c.h.
+// Note that there is some dummy C code at the top and bottom of the file
+// to fool text editors like VS Code into believing this is valid C code.
+// The actual instruction definitions start at // BEGIN BYTECODES //.
+// See Tools/cases_generator/README.md for more information.
+
 #include "Python.h"
 #include "pycore_abstract.h"      // _PyIndex_Check()
 #include "pycore_call.h"          // _PyObject_FastCallDictTstate()
@@ -4003,13 +4011,14 @@ dummy_func(
 // END BYTECODES //
 
     }
- error:;
- exception_unwind:;
- handle_eval_breaker:;
- resume_frame:;
- resume_with_error:;
- start_frame:;
- unbound_local_error:;
+ error:
+ exception_unwind:
+ handle_eval_breaker:
+ resume_frame:
+ resume_with_error:
+ start_frame:
+ unbound_local_error:
+    ;
 }
 
 // Families go below this point //

Python/generated_cases.c.h

@@ -6,6 +6,7 @@
 
 import argparse
 import io
+import os
 import re
 import sys
 
@@ -67,7 +68,7 @@ def write_cases(f: io.TextIOBase, instrs: list[InstDef]):
         for target in re.findall(r"(?:PREDICT|GO_TO_INSTRUCTION)\((\w+)\)", inst.block.text):
             predictions.add(target)
     indent = "        "
-    f.write("// This file is generated by Tools/scripts/generate_cases.py\n")
+    f.write(f"// This file is generated by {os.path.relpath(__file__)}\n")
     f.write("// Do not edit!\n")
     for instr in instrs:
         assert isinstance(instr, InstDef)