Add header-abi-checker for Vndk abi checks.

header-abi-dumper: dumps abi exported by source files for Vndk.
header-abi-linker: links abi dumps produced by header-abi-dumper.
header-abi-diff: compares linked dumps.

Test: mm -j64 showcommands > make_log in bionic/libc.
      This produced linked dumps in out/soong/.intermediates.
      Copied these dumps to
      prebuilts/abi-dumps/ndk/current/arm64/source-based/.
      Changed the abi and re-ran mm -j64 showcommands > make_log
      confirmed that the build reported compatibility breakge without
      actually failing (advisory mode).

Change-Id: Iccad6908fe68a80f47230751671d156893b96ead

android/paths.go

@@ -576,6 +576,30 @@ type ModuleOutPath struct {
 
 var _ Path = ModuleOutPath{}
 
+// PathForVndkRefDump returns an OptionalPath representing the path of the reference
+// abi dump for the given module. This is not guaranteed to be valid.
+func PathForVndkRefAbiDump(ctx ModuleContext, version, fileName string, vndkOrNdk, isSourceDump bool) OptionalPath {
+	archName := ctx.Arch().ArchType.Name
+	var sourceOrBinaryDir string
+	var vndkOrNdkDir string
+	var ext string
+	if isSourceDump {
+		ext = ".lsdump"
+		sourceOrBinaryDir = "source-based"
+	} else {
+		ext = ".bdump"
+		sourceOrBinaryDir = "binary-based"
+	}
+	if vndkOrNdk {
+		vndkOrNdkDir = "vndk"
+	} else {
+		vndkOrNdkDir = "ndk"
+	}
+	refDumpFileStr := "prebuilts/abi-dumps/" + vndkOrNdkDir + "/" + version + "/" +
+		archName + "/" + sourceOrBinaryDir + "/" + fileName + ext
+	return OptionalPathForSource(ctx, "", refDumpFileStr)
+}
+
 // PathForModuleOut returns a Path representing the paths... under the module's
 // output directory.
 func PathForModuleOut(ctx ModuleContext, paths ...string) ModuleOutPath {