Support `sdk_version: "current"` for the NDK.

We need to fall back to the old CRT objects since we aren't generating
those yet.

Test: Created a test module using "current", checked that it linked
      the libs from current.
Bug: None

Change-Id: I5fe170d7b26154da8877672ac2acb7da0262fe38
diff --git a/cc/binary.go b/cc/binary.go
index b029439..c16dae6 100644
--- a/cc/binary.go
+++ b/cc/binary.go
@@ -101,15 +101,24 @@
 				}
 				deps.CrtEnd = "crtend_android"
 			} else {
+				// TODO(danalbert): Add generation of crt objects.
+				// For `sdk_version: "current"`, we don't actually have a
+				// freshly generated set of CRT objects. Use the last stable
+				// version.
+				version := ctx.sdkVersion()
+				if version == "current" {
+					version = ctx.AConfig().PlatformSdkVersion()
+				}
+
 				if binary.static() {
-					deps.CrtBegin = "ndk_crtbegin_static." + ctx.sdkVersion()
+					deps.CrtBegin = "ndk_crtbegin_static." + version
 				} else {
 					if binary.static() {
-						deps.CrtBegin = "ndk_crtbegin_static." + ctx.sdkVersion()
+						deps.CrtBegin = "ndk_crtbegin_static." + version
 					} else {
-						deps.CrtBegin = "ndk_crtbegin_dynamic." + ctx.sdkVersion()
+						deps.CrtBegin = "ndk_crtbegin_dynamic." + version
 					}
-					deps.CrtEnd = "ndk_crtend_android." + ctx.sdkVersion()
+					deps.CrtEnd = "ndk_crtend_android." + version
 				}
 			}
 		}