tests: fix regressions.

Exit status 63 is documented for version-mismatch.
	* bootstrap.conf (gnulib_modules): Remove sysexits.
	* src/system.h (EX_MISMATCH): Define.
	* src/parse-gram.y (version_check): Use it instead of EX_CONFIG.

Missing includes.
	* tests/calc.at, tests/named-refs.at: Include assert.h.
(cherry picked from commit 459a57a90f)

src/system.h

@@ -52,7 +52,8 @@
 typedef size_t uintptr_t;
 #endif
 
-#include <sysexits.h>
+// Version mismatch.
+#define EX_MISMATCH 63
 
 /*---------.
 | Gnulib.  |