linux: Fix error when generating symbols.

Somehow strip would return 1 when a directory is passed, so we have to
wrap it in a script to avoid the error.

atom.gyp

@@ -636,7 +636,10 @@
                 # Gyp action requires a output file, add a fake one here.
                 '<(PRODUCT_DIR)/dummy_file',
               ],
-              'action': [ 'strip', '<@(_inputs)' ],
+              'action': [
+                'tools/posix/strip.sh',
+                '<@(_inputs)',
+              ],
             },
           ],
         }],  # OS=="linux"

tools/posix/strip.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+
+# Ignore errors from strip.
+strip "$@"
+
+exit 0