yasm: specify empty public header for assembly library

By specifying empty list in public header, unnecessary build dependency will be
removed from generated ninja files.

More detail in GN reference.
https://chromium.googlesource.com/chromium/src/+/master/tools/gn/docs/reference.md#public

Bug: 578477
Change-Id: I2321ae53376de907d05a59f14d3578a11b2be584
Reviewed-on: https://chromium-review.googlesource.com/1037063
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#555026}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: cab48032c45695c73b202af7d472a52808d551ca
diff --git a/yasm_assemble.gni b/yasm_assemble.gni
index 07bf5f9..f94fa6b 100644
--- a/yasm_assemble.gni
+++ b/yasm_assemble.gni
@@ -189,6 +189,9 @@
 
     sources = get_target_outputs(":$action_name")
 
+    # Do not publicize any header to remove build dependency.
+    public = []
+
     deps = [
       ":$action_name",
     ]