Various cleanups (#101)

* Rename BUILD files to match the rest of the repo.

* Move host tests to a specific subpackage

* Add a gitignore file

.gitignore

@@ -0,0 +1,2 @@
+MODULE.bazel.lock
+bazel-*

tests/BUILD

@@ -1,11 +1,10 @@
 load("//:version.bzl", "version")
-load("//host:constraints.bzl", "HOST_CONSTRAINTS")
 
 package(default_visibility = ["//visibility:private"])
 
 # This is a quick hack to make sure that version.bzl agrees with MODULE.bazel
 # It only works from Linux, but that is sufficient, becuase we do a presubmit
-# run linux, so we will still catch a mismatch.
+# run on linux, so we will still catch a mismatch.
 genrule(
     name = "versions_match",
     outs = ["found_it"],
@@ -20,10 +19,3 @@ genrule(
         "//:MODULE.bazel",
     ],
 )
-
-sh_test(
-    name = "host_constraints_test",
-    srcs = ["host_constraints_test.sh"],
-    env = {"ACTUAL_HOST_CONSTRAINTS": repr(HOST_CONSTRAINTS)},
-    env_inherit = ["EXPECTED_HOST_CONSTRAINTS"],
-)

tests/host/BUILD

@@ -0,0 +1,10 @@
+load("//host:constraints.bzl", "HOST_CONSTRAINTS")
+
+package(default_visibility = ["//visibility:private"])
+
+sh_test(
+    name = "host_constraints_test",
+    srcs = ["host_constraints_test.sh"],
+    env = {"ACTUAL_HOST_CONSTRAINTS": repr(HOST_CONSTRAINTS)},
+    env_inherit = ["EXPECTED_HOST_CONSTRAINTS"],
+)