Fix GCC build failure with C89-compatible loop declaration

[Copilot]

The Ubuntu GCC job failed because XCBuildConfiguration.m declares a loop variable in the for initializer, which the compiler’s pre-C99 mode rejects.

• Change: Declare the index before the loop and reuse it in the initializer:

  NSUInteger i;
  for (i = 0; i < [value length]; i++)