code_clean: exclude BLI_strict_flags.h from removal

As this is only added to set strict warnings, cleaning logic would
remove as the compilers output is unchanged.

Support excluding headers from removal, others can be added if needed.

tools/utils_maintenance/code_clean.py

@@ -1465,6 +1465,14 @@ class edit_generators:
         # Before committing these changes all supported platforms should be tested to compile without problems.
         is_default = False
 
+        @staticmethod
+        def _header_exclude(f_basename: str) -> str:
+            # This header only exists to add additional warnings, removing it doesn't impact generated output.
+            # Skip this file.
+            if f_basename == "BLI_strict_flags.h":
+                return True
+            return False
+
         @staticmethod
         def _header_guard_from_filename(f: str) -> str:
             return '__%s__' % os.path.basename(f).replace('.', '_').upper()
@@ -1481,6 +1489,10 @@ class edit_generators:
                     os.path.join(SOURCE_DIR, 'source'),
                     ('.h', '.hh', '.inl', '.hpp', '.hxx'),
             ):
+                f_basename = os.path.basename(f)
+                if cls._header_exclude(f_basename):
+                    continue
+
                 with open(f, 'r', encoding='utf-8') as fh:
                     data = fh.read()
 
@@ -1521,7 +1533,12 @@ class edit_generators:
             # Remove include.
             for match in re.finditer(r"^(([ \t]*#\s*include\s+\")([^\"]+)(\"[^\n]*\n))", data, flags=re.MULTILINE):
                 header_name = match.group(3)
-                header_guard = cls._header_guard_from_filename(header_name)
+                # Use in case the include has a leading path.
+                header_basename = os.path.basename(header_name)
+                if cls._header_exclude(header_basename):
+                    continue
+
+                header_guard = cls._header_guard_from_filename(header_basename)
                 edits.append(Edit(
                     span=match.span(),
                     content='',  # Remove the header.