bp2build: export some cc toolchain flags into Starlark.

This CL exports common/global/device/host clang/ld/ldd flags
from their Ninja variable initialization locations in
cc/config/global.go and cc/config/clang.go to make Bazel's cc_toolchain
and Soong's cc actions more consistent with each other.

This does not handle env-dependent or arch-specific toolchain flags
yet (logic in compiler.go and linker.go).

Test: TH
Bug: 187086342
Bug: 187084737
Bug: 186628704
Bug: 187857770
Change-Id: Ie403d7cd23f35160897b9dd902c799cbf1bd7f0c

bp2build/conversion_test.go

@@ -79,9 +79,33 @@ func TestCreateBazelFiles_QueryView_AddsTopLevelFiles(t *testing.T) {
 	}
 }
 
-func TestCreateBazelFiles_Bp2Build_CreatesNoFilesWithNoTargets(t *testing.T) {
-	files := CreateBazelFiles(map[string]RuleShim{}, map[string]BazelTargets{}, Bp2Build)
-	if len(files) != 0 {
-		t.Errorf("Expected no files, got %d", len(files))
+func TestCreateBazelFiles_Bp2Build_CreatesDefaultFiles(t *testing.T) {
+	files := CreateSoongInjectionFiles()
+
+	expectedFilePaths := []bazelFilepath{
+		{
+			dir:      "cc_toolchain",
+			basename: "BUILD",
+		},
+		{
+			dir:      "cc_toolchain",
+			basename: "constants.bzl",
+		},
+	}
+
+	if len(files) != len(expectedFilePaths) {
+		t.Errorf("Expected %d file, got %d", len(expectedFilePaths), len(files))
+	}
+
+	for i := range files {
+		actualFile, expectedFile := files[i], expectedFilePaths[i]
+
+		if actualFile.Dir != expectedFile.dir || actualFile.Basename != expectedFile.basename {
+			t.Errorf("Did not find expected file %s/%s", actualFile.Dir, actualFile.Basename)
+		}
+
+		if expectedFile.basename != "BUILD" && actualFile.Contents == "" {
+			t.Errorf("Contents of %s unexpected empty.", actualFile)
+		}
 	}
 }