Silence some warnings on GCC 4.9

src/libmain/stack.cc

@@ -32,7 +32,7 @@ static void sigsegvHandler(int signo, siginfo_t * info, void * ctx)
         if (diff < 0) diff = -diff;
         if (diff < 4096) {
             char msg[] = "error: stack overflow (possible infinite recursion)\n";
-            write(2, msg, strlen(msg));
+            (void) write(2, msg, strlen(msg));
             _exit(1); // maybe abort instead?
         }
     }

src/libstore/build.cc

@@ -1976,9 +1976,11 @@ void DerivationGoal::runChild()
 
             /* Set the hostname etc. to fixed values. */
             char hostname[] = "localhost";
-            sethostname(hostname, sizeof(hostname));
+            if (sethostname(hostname, sizeof(hostname)) == -1)
+                throw SysError("cannot set host name");
             char domainname[] = "(none)"; // kernel default
-            setdomainname(domainname, sizeof(domainname));
+            if (setdomainname(domainname, sizeof(domainname)) == -1)
+                throw SysError("cannot set domain name");
 
             /* Make all filesystems private.  This is necessary
                because subtrees may have been mounted as "shared"

src/libstore/remote-store.cc

@@ -109,7 +109,7 @@ void RemoteStore::connectToDaemon()
        applications... */
     AutoCloseFD fdPrevDir = open(".", O_RDONLY);
     if (fdPrevDir == -1) throw SysError("couldn't open current directory");
-    chdir(dirOf(socketPath).c_str());
+    if (chdir(dirOf(socketPath).c_str()) == -1) throw SysError("couldn't change current directory");
     Path socketPathRel = "./" + baseNameOf(socketPath);
 
     struct sockaddr_un addr;

src/nix-daemon/nix-daemon.cc

@@ -698,7 +698,8 @@ static PeerInfo getPeerInfo(int remote)
 
 static void daemonLoop(char * * argv)
 {
-    chdir("/");
+    if (chdir("/") == -1)
+        throw SysError("cannot change current directory");
 
     /* Get rid of children automatically; don't let them become
        zombies. */
@@ -728,7 +729,8 @@ static void daemonLoop(char * * argv)
         /* Urgh, sockaddr_un allows path names of only 108 characters.
            So chdir to the socket directory so that we can pass a
            relative path name. */
-        chdir(dirOf(socketPath).c_str());
+        if (chdir(dirOf(socketPath).c_str()) == -1)
+            throw SysError("cannot change current directory");
         Path socketPathRel = "./" + baseNameOf(socketPath);
 
         struct sockaddr_un addr;
@@ -748,7 +750,8 @@ static void daemonLoop(char * * argv)
         if (res == -1)
             throw SysError(format("cannot bind to socket ‘%1%’") % socketPath);
 
-        chdir("/"); /* back to the root */
+        if (chdir("/") == -1) /* back to the root */
+            throw SysError("cannot change current directory");
 
         if (listen(fdSocket, 5) == -1)
             throw SysError(format("cannot listen on socket ‘%1%’") % socketPath);