Implement infrastructure around new lexer

The lexer itself is very much incomplete, but this is intended to be a
safe point to revert to should further implementation go south.

src/asm/warning.c

@@ -204,7 +204,7 @@ void verror(const char *fmt, va_list args, char const *flag)
 	fstk_Dump();
 	fprintf(stderr, flag ? ": [-Werror=%s]\n    " : ":\n    ", flag);
 	vfprintf(stderr, fmt, args);
-	fstk_DumpStringExpansions();
+	lexer_DumpStringExpansions();
 	nbErrors++;
 }
 
@@ -256,7 +256,7 @@ void warning(enum WarningID id, char const *fmt, ...)
 	fstk_Dump();
 	fprintf(stderr, ": [-W%s]\n    ", flag);
 	vfprintf(stderr, fmt, args);
-	fstk_DumpStringExpansions();
+	lexer_DumpStringExpansions();
 
 	va_end(args);
 }