X11 has an attribute that was causing function declarations to be
missed.
These definitions exist in XLibint.h
eg:
```cpp
extern void _XEatData(
Display* /* dpy */,
unsigned long /* n */
) _X_COLD;
```
This `_X_COLD` attribute was causing these function definitions to get
missed.
This is very useful for extracting function definitions for thunks.
Keep it in upstream to not get lost.
Sometimes it can munge a definition but it is usually fine.
Ryan Houdek