Set target_arch to ia32 instead of x86_64 on 32bit userland 64bit kernel systems.

build/common.gypi

Index: build/common.gypi
===================================================================
--- build/common.gypi	(revision 13364)
+++ build/common.gypi	(working copy)
@@ -107,11 +107,12 @@
             # NOTE: currently only nacl is generating gyp files on an arm board.
             #    The arm.* -> arm substitution in chrome's common.gypi isn't
             #    appropriate in that context as we actually use target_arch==arm
-            #    to me x86 -> arm cross compile. When actually running on an arm
-            #    board, we'll generate ia32 for now, so that the generation
+            #    to mean x86 -> arm cross compile. When actually running on an
+            #    arm board, we'll generate ia32 for now, so that the generation
             #    succeeds.
             'target_arch%':
-              '<!(uname -m | sed -e "s/i.86/ia32/;s/x86_64/x64/;s/amd64/x64/;s/arm.*/ia32/")'
+                '<!(echo "<!pymod_do_main(detect_nacl_host_arch)" | sed -e "s/arm.*/ia32/")',
+
           }, {  # OS!="linux"
             'target_arch%': 'ia32',
           }],