Don't create SDK variants for native bridge modules

Native bridge modules never need to build against NDK stubs, so
don't create SDK variants.  Also clear the sdk_version property
for modules that don't have SDK variants so that later code doesn't
use it to trigger SDK behaviors.

Test: m checkbuild
Change-Id: I1920fa82e9fab06235f01a62624382efa16cc6e3
diff --git a/cc/sdk.go b/cc/sdk.go
index ec57f06..2c3fec3 100644
--- a/cc/sdk.go
+++ b/cc/sdk.go
@@ -38,18 +38,31 @@
 			ctx.CreateVariations("sdk")
 		} else if m.UseSdk() || m.SplitPerApiLevel() {
 			modules := ctx.CreateVariations("", "sdk")
+
+			// Clear the sdk_version property for the platform (non-SDK) variant so later code
+			// doesn't get confused by it.
 			modules[0].(*Module).Properties.Sdk_version = nil
+
+			// Mark the SDK variant.
 			modules[1].(*Module).Properties.IsSdkVariant = true
 
 			if ctx.Config().UnbundledBuildApps() {
+				// For an unbundled apps build, hide the platform variant from Make.
 				modules[0].(*Module).Properties.HideFromMake = true
 				modules[0].(*Module).Properties.PreventInstall = true
 			} else {
+				// For a platform build, mark the SDK variant so that it gets a ".sdk" suffix when
+				// exposed to Make.
 				modules[1].(*Module).Properties.SdkAndPlatformVariantVisibleToMake = true
 				modules[1].(*Module).Properties.PreventInstall = true
 			}
 			ctx.AliasVariation("")
 		} else {
+			if m, ok := ctx.Module().(*Module); ok {
+				// Clear the sdk_version property for modules that don't have an SDK variant so
+				// later code doesn't get confused by it.
+				m.Properties.Sdk_version = nil
+			}
 			ctx.CreateVariations("")
 			ctx.AliasVariation("")
 		}