Pass filename mappings to C++ and Java extractors.

Android builds by default put artifacts into out/ subdirectory of
the source tree, causing the extractor to record their names as
relative. The indexer considers such files as sources, which is wrong.
Fortunately, the extractor can be fed a set of filename rewriting
rules (see build/tools/vnames.json).
Also, undo previous unsuccessful attempt use to absolute path for the
output directory to distinguish between source code and artifacts.

Bug: 141385476
Test: run the build, inspect compilation units of the kzip file
Change-Id: I89ec3aed8fd14f43ea6e0b226d54f643346f6125
diff --git a/cc/builder.go b/cc/builder.go
index b353814..c4f65da 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -224,12 +224,13 @@
 
 	_ = pctx.SourcePathVariable("cxxExtractor",
 		"prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/cxx_extractor")
+	_ = pctx.SourcePathVariable("kytheVnames", "build/soong/vnames.json")
 	_ = pctx.VariableFunc("kytheCorpus",
 		func(ctx android.PackageVarContext) string { return ctx.Config().XrefCorpusName() })
 	kytheExtract = pctx.StaticRule("kythe",
 		blueprint.RuleParams{
-			Command:     "rm -f $out && KYTHE_CORPUS=${kytheCorpus} KYTHE_OUTPUT_FILE=$out $cxxExtractor $cFlags $in ",
-			CommandDeps: []string{"$cxxExtractor"},
+			Command:     "rm -f $out && KYTHE_CORPUS=${kytheCorpus} KYTHE_OUTPUT_FILE=$out KYTHE_VNAMES=$kytheVnames $cxxExtractor $cFlags $in ",
+			CommandDeps: []string{"$cxxExtractor", "$kytheVnames"},
 		},
 		"cFlags")
 )