One more fix for icu.gyp.

icu.gyp

diff --git a/icu.gyp b/icu.gyp
index 1bb7cf7..16b300e 100644
--- a/icu.gyp
+++ b/icu.gyp
@@ -43,6 +43,7 @@
         'include_dirs': [
           'source/common',
           'source/i18n',
+          'genfiles/arch/<(OS)/common/include',
         ],
         'msvs_disabled_warnings': [4005, 4355, 4996],
       },