Add micro_layer_common

Depending on this for layers won't bring in the the validation layer
error strings, saving disk space.

MA-545 #comment
Test: vim2:go/magma-tps#L1

Change-Id: I5f33ef69aa3547e9905c6e194988df50bf3bd7ad
diff --git a/layers/BUILD.gn b/layers/BUILD.gn
index 01e9462..6dce979 100644
--- a/layers/BUILD.gn
+++ b/layers/BUILD.gn
@@ -71,6 +71,22 @@
   ldflags = [ "-static-libstdc++" ]
 }
 
+# This source_set doesn't include the validation layer strings by default, though including some
+# files (e.g. vk_layer_logging.h or vk_layer_utils.h) might still bring them in to a target.
+source_set("micro_layer_common") {
+  public_configs = [
+    ":layer_include_config",
+  ]
+  sources = [
+    "vk_layer_extension_utils.cpp",
+    "vk_layer_table.cpp",
+  ]
+  public_deps = [
+    "../:extra_vulkan_headers",
+    "../:vulkan",
+  ]
+}
+
 source_set("layer_common") {
   public_configs = [
     ":layer_include_config",