Silence warnings about seteuid return value.

Closes #483.

EnvScreen.c

@@ -49,9 +49,9 @@ void EnvScreen_scan(InfoScreen* this) {
    Panel_prune(panel);
 
    uid_t euid = geteuid();
-   seteuid(getuid());
+   (void) seteuid(getuid());
    char *env = Platform_getProcessEnv(this->process->pid);
-   seteuid(euid);
+   (void) seteuid(euid);
    if (env) {
       for (char *p = env; *p; p = strrchr(p, 0)+1)
          InfoScreen_addLine(this, p);

Process.c

@@ -518,10 +518,10 @@ void Process_toggleTag(Process* this) {
 
 bool Process_setPriority(Process* this, int priority) {
    uid_t euid = geteuid();
-   seteuid(getuid());
+   (void) seteuid(getuid());
    int old_prio = getpriority(PRIO_PROCESS, this->pid);
    int err = setpriority(PRIO_PROCESS, this->pid, priority);
-   seteuid(euid);
+   (void) seteuid(euid);
    if (err == 0 && old_prio != getpriority(PRIO_PROCESS, this->pid)) {
       this->nice = priority;
    }
@@ -534,9 +534,9 @@ bool Process_changePriorityBy(Process* this, size_t delta) {
 
 void Process_sendSignal(Process* this, size_t sgn) {
    uid_t euid = geteuid();
-   seteuid(getuid());
+   (void) seteuid(getuid());
    kill(this->pid, (int) sgn);
-   seteuid(euid);
+   (void) seteuid(euid);
 }
 
 long Process_pidCompare(const void* v1, const void* v2) {

Settings.c

@@ -167,9 +167,9 @@ static bool Settings_read(Settings* this, const char* fileName) {
    FILE* fd;
    uid_t euid = geteuid();
 
-   seteuid(getuid());
+   (void) seteuid(getuid());
    fd = fopen(fileName, "r");
-   seteuid(euid);
+   (void) seteuid(euid);
    if (!fd)
       return false;
    
@@ -277,9 +277,9 @@ bool Settings_write(Settings* this) {
    FILE* fd;
    uid_t euid = geteuid();
 
-   seteuid(getuid());
+   (void) seteuid(getuid());
    fd = fopen(this->filename, "w");
-   seteuid(euid);
+   (void) seteuid(euid);
    if (fd == NULL) {
       return false;
    }
@@ -366,7 +366,7 @@ Settings* Settings_new(int cpuCount) {
       }
       legacyDotfile = String_cat(home, "/.htoprc");
       uid_t euid = geteuid();
-      seteuid(getuid());
+      (void) seteuid(getuid());
       (void) mkdir(configDir, 0700);
       (void) mkdir(htopDir, 0700);
       free(htopDir);
@@ -379,7 +379,7 @@ Settings* Settings_new(int cpuCount) {
          free(legacyDotfile);
          legacyDotfile = NULL;
       }
-      seteuid(euid);
+      (void) seteuid(euid);
    }
    this->colorScheme = 0;
    this->changed = false;

TraceScreen.c

@@ -95,7 +95,7 @@ bool TraceScreen_forkTracer(TraceScreen* this) {
    this->child = fork();
    if (this->child == -1) return false;
    if (this->child == 0) {
-      seteuid(getuid());
+      (void) seteuid(getuid());
       dup2(this->fdpair[1], STDERR_FILENO);
       int ok = fcntl(this->fdpair[1], F_SETFL, O_NONBLOCK);
       if (ok != -1) {