Adding support to build with linux toolchain

Change-Id: I5adf7b8204e82e029ffef8691920325ad058bd38
diff --git a/BUILD.gn b/BUILD.gn
index 649a3dd..992bbf7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -46,4 +46,9 @@
   deps = [
     "//third_party/gflags",
   ]
+
+  if (current_os == "linux") {
+    defines = [ "HAVE_SYSCALL_H" ]
+    cflags_cc = [ "-Wno-sign-compare" ]
+  }
 }