[tint][gn] Fix include_dirs in tint_common_config

Fix the gen dir - this was completely wrong under chromium.
Remove all the spirv include directories. Targets that need SPIR-V now properly explicitly depend on it.

Change-Id: I479237c31d0ce93029eba56c3e4510bc250ec90d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/164240
Kokoro: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/tint/BUILD.gn b/src/tint/BUILD.gn
index 6f78959..f8fe3f2 100644
--- a/src/tint/BUILD.gn
+++ b/src/tint/BUILD.gn
@@ -42,13 +42,13 @@
 # Common - Configs, etc. shared across targets
 ###############################################################################
 
+# tint_gen_dir is the relative path of tint_root_dir to '//', under root_gen_dir
+tint_gen_dir = "${root_gen_dir}/" + rebase_path("${tint_root_dir}", "//")
+
 config("tint_common_config") {
   include_dirs = [
-    "${target_gen_dir}",
-    "${tint_root_dir}/",
-    "${tint_spirv_headers_dir}/include",
-    "${tint_spirv_tools_dir}/",
-    "${tint_spirv_tools_dir}/include",
+    "${tint_root_dir}",
+    "${tint_gen_dir}",
   ]
 }
 
@@ -129,7 +129,6 @@
   include_dirs = [
     "${tint_root_dir}/",
     "${tint_root_dir}/include/",
-    "${tint_spirv_headers_dir}/include",
   ]
 }