Move ForkExecveAndWaitForCompletion to util.h

In the follow up patch this function will also be used in
first_stage_init.

Bug: 287593065
Test: m
Change-Id: Id805f8523596c26ed262d89aa652b27184b612c1
diff --git a/init/util.h b/init/util.h
index 2d02182..aa24123 100644
--- a/init/util.h
+++ b/init/util.h
@@ -117,5 +117,10 @@
 // (.rc == .0rc for ranking purposes)
 std::vector<std::string> FilterVersionedConfigs(const std::vector<std::string>& configs,
                                                   int active_sdk);
+
+// Forks, executes the provided program in the child, and waits for the completion in the parent.
+// Child's stderr is captured and logged using LOG(ERROR).
+bool ForkExecveAndWaitForCompletion(const char* filename, char* const argv[]);
+
 }  // namespace init
 }  // namespace android