Kernel: Fix pledge syscall applying new pledges when it fails (#2076)

If the exec promises fail to apply, then the normal promises should
not apply either. Add a test for this fixed functionality.

Tests/Kernel/pledge-test-failures.cpp

@@ -0,0 +1,25 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    int res = pledge("stdio unix rpath", "stdio");
+    if (res < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    res = pledge("stdio unix", "stdio unix");
+    if (res >= 0) {
+        fprintf(stderr, "second pledge should have failed\n");
+        return 1;
+    }
+
+    res = pledge("stdio rpath", "stdio");
+    if (res < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    return 0;
+}