Default to building for the same architecture as the build host.

BUG=24766

Review URL: http://codereview.chromium.org/271113


git-svn-id: http://src.chromium.org/svn/trunk/src/build@29230 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -35,8 +35,19 @@
       # builds).
       'buildtype%': 'Dev',
 
-      # The architecture that we're building on.
-      'target_arch%': 'ia32',
+      # Compute the architecture that we're building for. Default to the
+      # architecture that we're building on.
+      'conditions': [
+        [ 'OS=="linux"', {
+          # This handles the Linux platforms we generally deal with. Anything
+          # else gets passed through, which probably won't work very well; such
+          # hosts should pass an explicit target_arch to gyp.
+          'target_arch%':
+            '<!(uname -m | sed -e "s/i.86/ia32/;s/x86_64/x64/;s/arm.*/arm/")'
+        }, {  # OS!="linux"
+          'target_arch%': 'ia32',
+        }],
+      ],
 
       # We do want to build Chromium with Breakpad support in certain
       # situations. I.e. for Chrome bot.