libstore: move setPersonality to linux platform

it doesn't do anything anywhere else, and personality setup is not a
critical operation (all it does is change which arch uname returns).

Change-Id: I39d7fcc4916e6882e49191d2294f9b7ee0dbbcd0

lix/libstore/build/local-derivation-goal.cc

@@ -1157,8 +1157,6 @@ void LocalDerivationGoal::runChild()
         /* Close all other file descriptors. */
         closeExtraFDs();
 
-        setPersonality(drv->platform);
-
         /* Disable core dumps by default. */
         struct rlimit limit = { 0, RLIM_INFINITY };
         if (settings.enableCoreDumps) {

lix/libstore/platform/linux.cc

@@ -1,3 +1,4 @@
+#include "build/personality.hh"
 #include "lix/libstore/build/worker.hh"
 #include "lix/libutil/c-calls.hh"
 #include "lix/libutil/cgroup.hh"
@@ -1229,6 +1230,8 @@ bool LinuxLocalDerivationGoal::prepareChildSetup()
         }
     }
 
+    setPersonality(drv->platform);
+
     return false;
 }