Do not chmod the symlink target when a prebuilt binary is symlinked.

It may be in a source tree that isn't writable. Instead check that
the target is executable.

Test: m
Test: chmod a-x system/sepolicy/tools/insertkeys.py && \
  rm -rf out/host out/soong/host && \
  m insertkeys.py
  Check that it fails with the expected error message.
Fixes: 169375644
Change-Id: I402d029dba45783127586ad9749c90012afe891d
diff --git a/core/soong_cc_prebuilt.mk b/core/soong_cc_prebuilt.mk
index a0315a5..f98253d 100644
--- a/core/soong_cc_prebuilt.mk
+++ b/core/soong_cc_prebuilt.mk
@@ -149,11 +149,14 @@
 $(LOCAL_BUILT_MODULE): $(LOCAL_PREBUILT_MODULE_FILE)
 ifeq ($(LOCAL_IS_HOST_MODULE) $(if $(filter EXECUTABLES SHARED_LIBRARIES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),true,),true true)
 	$(copy-or-link-prebuilt-to-target)
+  ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
+	[ -x $@ ] || $(call echo-error,$@,Target of symlink is not executable)
+  endif
 else
 	$(transform-prebuilt-to-target)
-endif
-ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
+  ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
 	$(hide) chmod +x $@
+  endif
 endif
 
 ifndef LOCAL_IS_HOST_MODULE
diff --git a/core/soong_rust_prebuilt.mk b/core/soong_rust_prebuilt.mk
index b54f300..2f4c6e7 100644
--- a/core/soong_rust_prebuilt.mk
+++ b/core/soong_rust_prebuilt.mk
@@ -59,11 +59,14 @@
 $(LOCAL_BUILT_MODULE): $(LOCAL_PREBUILT_MODULE_FILE)
 ifeq ($(LOCAL_IS_HOST_MODULE) $(if $(filter EXECUTABLES SHARED_LIBRARIES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),true,),true true)
 	$(copy-or-link-prebuilt-to-target)
+  ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
+	[ -x $@ ] || $(call echo-error,$@,Target of symlink is not executable)
+  endif
 else
 	$(transform-prebuilt-to-target)
-endif
-ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
+  ifneq ($(filter EXECUTABLES NATIVE_TESTS,$(LOCAL_MODULE_CLASS)),)
 	$(hide) chmod +x $@
+  endif
 endif
 
 ifndef LOCAL_IS_HOST_MODULE