Make minidump_stackwalk compile with target_arch=ia32 on a linux x64 host.

This is necessary for the perf bots to build minidump_stackwalk which will
allow us to have stack traces when perf tests crash.

BUG=223572
TEST=GYP_DEFINES="branding=Chrome buildtype=Official target_arch=ia32 component=static_library" gclient runhooks && ninja -C out/Release minidump_stackwalk

Review URL: https://chromiumcodereview.appspot.com/23064014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@218622 0039d316-1c4b-4281-b951-d872f2087c98

breakpad/breakpad_tools.gypi

@@ -14,6 +14,11 @@
           'ldflags!': ['-m32'],
           'cflags': ['-O2'],
           'include_dirs!': ['/usr/include32'],
+          'conditions': [
+            ['target_arch=="ia32" and sysroot!=""', {
+              'cflags!': ['--sysroot=<(sysroot)'],
+            }],
+          ],
         }],
       ],
     }],