apex: Install nativeTest with soong_cc_prebuilt.mk

This commit switches the build rule for APEX nativeTests from
`$(BUILD_PREBUILT)` to `soong_cc_prebuilt.mk`.  Since these are not real
prebuilts, `soong_cc_prebuilt.mk` should be sufficient.

Using `soong_cc_prebuilt.mk` also fixes a problem reported by prebuilt
ELF checker because `LOCAL_SHARED_LIBRARIES` are not generated for
nativeTests.

Bug: 139525855
Test: lunch aosp_walleye-userdebug && make check-elf-files
Change-Id: I7bfc29f9c2708896dad4e7cfc214480e1205a51e
diff --git a/apex/apex.go b/apex/apex.go
index 1e99ff8..909852e 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1518,7 +1518,7 @@
 			fmt.Fprintln(w, "LOCAL_SOONG_DEX_JAR :=", fi.builtFile.String())
 			fmt.Fprintln(w, "LOCAL_DEX_PREOPT := false")
 			fmt.Fprintln(w, "include $(BUILD_SYSTEM)/soong_java_prebuilt.mk")
-		} else if fi.class == nativeSharedLib || fi.class == nativeExecutable {
+		} else if fi.class == nativeSharedLib || fi.class == nativeExecutable || fi.class == nativeTest {
 			fmt.Fprintln(w, "LOCAL_MODULE_STEM :=", fi.builtFile.Base())
 			if cc, ok := fi.module.(*cc.Module); ok {
 				if cc.UnstrippedOutputFile() != nil {