Revert of Use -fno-delete-null-pointer-checks with gcc builds

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index a84b29d0d72e0bdaafd9d5b25e384d5b0690574a..4e2c2b9aacb7fb93d69c0ff84cce099e0e81a49a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -321,13 +321,6 @@
   }
   if (is_android && v8_android_log_stdout) {
     defines += [ "V8_ANDROID_LOG_STDOUT" ]
-  }
-  if (!is_win && !is_clang) {
-    # GCC 6+ can optimize away pointer comparisons to null. This is
-    # problematic as V8 encodes Values through tagged pointers and comparisons
-    # with 0 are actually necessary in many cases. As a temporary Workaround
-    # we disable this optimization. See: https://crbug.com/v8/3782
-    cflags += [ "-fno-delete-null-pointer-checks" ]
   }
 
   # TODO(jochen): Support v8_enable_prof on Windows.