C23-compliant preprocessor

The section **6.10 Preprocessing directives** of the C standard defines the requirements to the C preprocessor. We should fulfill them.

## TODO
- [ ] #525
- [x] #538
- [ ] 6.10 Preprocessing directives
- [ ] 6.10.1 Conditional inclusion
- [x] #532
- [x] #534
- [x] 6.10.2 Source file inclusion
- [ ] 6.10.3 Binary resource inclusion
- [ ] #174
- [ ] 6.10.4 Macro replacement
- [x] #429
- [ ] #541
- [ ] #542
- [x] 6.10.4.1 Argument substitution
- [x] 6.10.4.2 The # operator
- [x] 6.10.4.3 The ## operator
- [ ] 6.10.4.4 Rescanning and further replacement
- [x] 6.10.4.5 Scope of macro definitions
- [ ] 6.10.5 Line control
- [ ] 6.10.6 Diagnostic directives
- [x] `#error`
- [ ] `#warning`
- [x] 6.10.7 Pragma directive
- [x] 6.10.8 Null directive
- [ ] 6.10.9 Predefined macro names
- [ ] 6.10.9.1 Mandatory macros
- [ ] 6.10.9.2 Environment macros
- [ ] 6.10.9.3 Conditional feature macros
- [ ] 6.10.10 Pragma operator

Look for the number `77` in the code to find clues to implement this feature.