errno-list: errno_from_name() is pure but not const

Follow-up for 0c15577abe

src/basic/errno-list.c

@@ -9,28 +9,6 @@ static const struct errno_name* lookup_errno(register const char *str,
 
 #include "errno-from-name.inc"
 
-#if HAVE_STRERRORNAME_NP
-const char* errno_to_name(int id) {
-        if (id == 0) /* To stay in line with our own impl */
-                return NULL;
-
-        return strerrorname_np(ABS(id));
-}
-#else
-#include "errno-to-name.inc"
-
-const char* errno_to_name(int id) {
-
-        if (id < 0)
-                id = -id;
-
-        if ((size_t) id >= ELEMENTSOF(errno_names))
-                return NULL;
-
-        return errno_names[id];
-}
-#endif
-
 int errno_from_name(const char *name) {
         const struct errno_name *sc;
 
@@ -43,3 +21,25 @@ int errno_from_name(const char *name) {
         assert(sc->id > 0);
         return sc->id;
 }
+
+#if HAVE_STRERRORNAME_NP
+const char* errno_to_name(int id) {
+        if (id == 0) /* To stay in line with our own impl */
+                return NULL;
+
+        return strerrorname_np(ABS(id));
+}
+#else
+#  include "errno-to-name.inc"
+
+const char* errno_to_name(int id) {
+
+        if (id < 0)
+                id = -id;
+
+        if ((size_t) id >= ELEMENTSOF(errno_names))
+                return NULL;
+
+        return errno_names[id];
+}
+#endif

src/basic/errno-list.h

@@ -4,8 +4,7 @@
 #include "forward.h"
 
 const char* errno_to_name(int id);
-
-int errno_from_name(const char *name) _const_;
+int errno_from_name(const char *name) _pure_;
 
 static inline bool errno_is_valid(int n) {
         return n > 0 && n <= ERRNO_MAX;

src/basic/errno-util.h

@@ -52,7 +52,6 @@ static inline int negative_errno(void) {
          * It will suppress bogus gcc warnings in case it assumes 'errno' might
          * be 0 and thus the caller's error-handling might not be triggered. */
         assert_return(errno > 0, -EINVAL);
-
         return -errno;
 }