Add bp2build support for cc_prebuilt_object

Add bp2build support for cc_prebuilt_object to allow buiiding
musl crt objects that use prebuilt clang_rt.crtbegin and
clang_rt.crtend.

Bug: 259266326
Test: //extenral/musl:libc_musl builds
Change-Id: Ic2b0375bc6e7336d31c9e2cf51bdc2ea894185aa
diff --git a/bp2build/cc_prebuilt_object_conversion_test.go b/bp2build/cc_prebuilt_object_conversion_test.go
new file mode 100644
index 0000000..903c816
--- /dev/null
+++ b/bp2build/cc_prebuilt_object_conversion_test.go
@@ -0,0 +1,101 @@
+// Copyright 2022 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package bp2build
+
+import (
+	"fmt"
+	"testing"
+
+	"android/soong/cc"
+)
+
+func runCcPrebuiltObjectTestCase(t *testing.T, testCase Bp2buildTestCase) {
+	t.Helper()
+	description := fmt.Sprintf("cc_prebuilt_object: %s", testCase.Description)
+	testCase.ModuleTypeUnderTest = "cc_prebuilt_object"
+	testCase.ModuleTypeUnderTestFactory = cc.PrebuiltObjectFactory
+	testCase.Description = description
+	t.Run(description, func(t *testing.T) {
+		t.Helper()
+		RunBp2BuildTestCaseSimple(t, testCase)
+	})
+}
+
+func TestPrebuiltObject(t *testing.T) {
+	runCcPrebuiltObjectTestCase(t,
+		Bp2buildTestCase{
+			Description: "simple",
+			Filesystem: map[string]string{
+				"obj.o": "",
+			},
+			Blueprint: `
+cc_prebuilt_object {
+	name: "objtest",
+	srcs: ["obj.o"],
+	bazel_module: { bp2build_available: true },
+}`,
+			ExpectedBazelTargets: []string{
+				MakeBazelTarget("cc_prebuilt_object", "objtest", AttrNameToString{
+					"src": `"obj.o"`,
+				})},
+		})
+}
+
+func TestPrebuiltObjectWithArchVariance(t *testing.T) {
+	runCcPrebuiltObjectTestCase(t,
+		Bp2buildTestCase{
+			Description: "with arch variance",
+			Filesystem: map[string]string{
+				"obja.o": "",
+				"objb.o": "",
+			},
+			Blueprint: `
+cc_prebuilt_object {
+	name: "objtest",
+	arch: {
+		arm64: { srcs: ["obja.o"], },
+		arm: { srcs: ["objb.o"], },
+	},
+	bazel_module: { bp2build_available: true },
+}`, ExpectedBazelTargets: []string{
+				MakeBazelTarget("cc_prebuilt_object", "objtest", AttrNameToString{
+					"src": `select({
+        "//build/bazel/platforms/arch:arm": "objb.o",
+        "//build/bazel/platforms/arch:arm64": "obja.o",
+        "//conditions:default": None,
+    })`,
+				}),
+			},
+		})
+}
+
+func TestPrebuiltObjectMultipleSrcsFails(t *testing.T) {
+	runCcPrebuiltObjectTestCase(t,
+		Bp2buildTestCase{
+			Description: "fails because multiple sources",
+			Filesystem: map[string]string{
+				"obja": "",
+				"objb": "",
+			},
+			Blueprint: `
+cc_prebuilt_object {
+	name: "objtest",
+	srcs: ["obja.o", "objb.o"],
+	bazel_module: { bp2build_available: true },
+}`,
+			ExpectedErr: fmt.Errorf("Expected at most one source file"),
+		})
+}
+
+// TODO: nosrcs test