Make a few commands that were Unix-only no longer

Also clean up some more linux-specific (`setPersonality`) code in
alignment with recent best practices.

src/libstore/linux/personality.cc

@@ -0,0 +1,41 @@
+#include "personality.hh"
+#include "globals.hh"
+
+#include <sys/utsname.h>
+#include <sys/personality.h>
+
+#include <cstring>
+
+namespace nix::linux {
+
+void setPersonality(std::string_view system)
+{
+        /* Change the personality to 32-bit if we're doing an
+           i686-linux build on an x86_64-linux machine. */
+        struct utsname utsbuf;
+        uname(&utsbuf);
+        if ((system == "i686-linux"
+                && (std::string_view(SYSTEM) == "x86_64-linux"
+                    || (!strcmp(utsbuf.sysname, "Linux") && !strcmp(utsbuf.machine, "x86_64"))))
+            || system == "armv7l-linux"
+            || system == "armv6l-linux"
+            || system == "armv5tel-linux")
+        {
+            if (personality(PER_LINUX32) == -1)
+                throw SysError("cannot set 32-bit personality");
+        }
+
+        /* Impersonate a Linux 2.6 machine to get some determinism in
+           builds that depend on the kernel version. */
+        if ((system == "i686-linux" || system == "x86_64-linux") && settings.impersonateLinux26) {
+            int cur = personality(0xffffffff);
+            if (cur != -1) personality(cur | 0x0020000 /* == UNAME26 */);
+        }
+
+        /* Disable address space randomization for improved
+           determinism. */
+        int cur = personality(0xffffffff);
+        if (cur != -1) personality(cur | ADDR_NO_RANDOMIZE);
+}
+
+}

src/libstore/linux/personality.hh

@@ -0,0 +1,12 @@
+#pragma once
+///@file
+
+#include <string>
+
+namespace nix::linux {
+
+void setPersonality(std::string_view system);
+
+}
+
+