Use icu_gyp_path variable to reference ICU gyp file

src/d8.gyp

Index: src/d8.gyp
diff --git a/src/d8.gyp b/src/d8.gyp
index 15d342dece7699237eb88385a8d28fd4353308b3..c033fd7e4e47b00108b14a5282ffc0197516202a 100644
--- a/src/d8.gyp
+++ b/src/d8.gyp
@@ -81,13 +81,13 @@
         }],
         ['v8_enable_i18n_support==1', {
           'dependencies': [
-            '<(DEPTH)/third_party/icu/icu.gyp:icui18n',
-            '<(DEPTH)/third_party/icu/icu.gyp:icuuc',
+            '<(icu_gyp_path):icui18n',
+            '<(icu_gyp_path):icuuc',
           ],
         }],
         ['OS=="win" and v8_enable_i18n_support==1', {
           'dependencies': [
-            '<(DEPTH)/third_party/icu/icu.gyp:icudata',
+            '<(icu_gyp_path):icudata',
           ],
         }],
       ],