Remove matcha from WORKSPACE, tweak dual_cc_library

- Having matcha imported into the workspace was causing circular
  dependencies to surface in Verilator builds.
- To allow removing matcha from the workspace, reverse the way the
  select works in dual_cc_library: If the platform matches host, use the
  host library. Anything else is assumed to be a device platform.

Change-Id: I623b99509c78d6f9343bf26eadd84e0be342064f

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index e0a9784..9eb984c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -7,14 +7,6 @@
 
 workspace(name = "lowrisc_opentitan")
 
-# We import this into the workspace to pick up a Bazel platform rule.
-# Be careful about importing anything else from here, it's not likely
-# to actually be something you want to do.
-local_repository(
-     name = "matcha",
-     path = "../matcha",
-)
-
 # CRT is the Compiler Repository Toolkit.  It contains the configuration for
 # the windows compiler.
 load("//third_party/crt:repos.bzl", "crt_repos")

rules/BUILD

diff --git a/rules/BUILD b/rules/BUILD
index ca0e934..40059e4 100644
--- a/rules/BUILD
+++ b/rules/BUILD
@@ -10,3 +10,8 @@
     name = "opentitan_platform",
     values = {"platforms": OPENTITAN_PLATFORM},
 )
+
+config_setting(
+    name = "host_platform",
+    values = {"platforms":"@local_config_platform//:host"},
+)

rules/cross_platform.bzl

diff --git a/rules/cross_platform.bzl b/rules/cross_platform.bzl
index 2193e70..9075b27 100644
--- a/rules/cross_platform.bzl
+++ b/rules/cross_platform.bzl
@@ -88,8 +88,7 @@
     native.alias(
         name = name,
         actual = select({
-            on_device_config_setting: dual_cc_device_library_of(name),
-            "@matcha//rules:sparrow_platform": dual_cc_device_library_of(name),
-            "//conditions:default": off_device_name,
+            "//rules:host_platform": off_device_name,
+            "//conditions:default": dual_cc_device_library_of(name),
         }),
     )