Allow NDK static libraries to use the NDK sysroot.

Building a static library for the NDK only requires that the NDK
headers be available. Currently, A module with both
`static_ndk_lib: true` and `sdk_version: something` will have a cyclic
dependency since it both needs the NDK and is in the NDK. Create two
NDK timestamp files: one for the isolated parts of the NDK (headers
and stub libraries), and another for the full sysroot with the static
libraries.

Test: set static_ndk_lib on compiler-rt-extras, make ndk
Bug: None
Change-Id: Iab50ffa0e4cbf4cd164f376e15281030c7aad984
diff --git a/cc/compiler.go b/cc/compiler.go
index 40dbea4..4eae898 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -522,7 +522,7 @@
 	if ctx.useSdk() {
 		// The NDK sysroot timestamp file depends on all the NDK sysroot files
 		// (headers and libraries).
-		return android.Paths{getNdkSysrootTimestampFile(ctx)}
+		return android.Paths{getNdkBaseTimestampFile(ctx)}
 	}
 	return nil
 }