Fix error-related issues (#773)

* Mark `error` as a `format` function, to properly scan its format

* Fix the call to error() from parser.y:
  - Use '%s' to avoid passing an arbitrary format
  - Simplify yyerror overall

* Fix size parameter of %.*s format being an int... bonkers standard.

* Report the number of arguments required and provided on a STRFMT mismatch

* Add an assert to check for a very unlikely bug

include/asm/warning.h

@@ -48,7 +48,7 @@ void processWarningFlag(char const *flag);
  * Used to warn the user about problems that don't prevent the generation of
  * valid code.
  */
-void warning(enum WarningID id, const char *fmt, ...);
+void warning(enum WarningID id, const char *fmt, ...) format_(printf, 2, 3);
 
 /*
  * Used for errors that compromise the whole assembly process by affecting the
@@ -57,7 +57,7 @@ void warning(enum WarningID id, const char *fmt, ...);
  * It is also used when the assembler goes into an invalid state (for example,
  * when it fails to allocate memory).
  */
-_Noreturn void fatalerror(const char *fmt, ...);
+_Noreturn void fatalerror(const char *fmt, ...) format_(printf, 1, 2);
 
 /*
  * Used for errors that make it impossible to assemble correctly, but don't
@@ -65,6 +65,6 @@ _Noreturn void fatalerror(const char *fmt, ...);
  * get a list of all errors at the end, making it easier to fix all of them at
  * once.
  */
-void error(const char *fmt, ...);
+void error(const char *fmt, ...) format_(printf, 1, 2);
 
 #endif