Another mac fix

Test: make (on linux)
Change-Id: I3f0561f3a1fc08dad5d3dd8ba860da56b51d273c
diff --git a/tools/bit/command.h b/tools/bit/command.h
index eb0b88f..fb44900 100644
--- a/tools/bit/command.h
+++ b/tools/bit/command.h
@@ -54,5 +54,8 @@
  */
 int run_command(const Command& command);
 
+// Mac OS doesn't have execvpe. This is the same as execvpe.
+int exec_with_path_search(const char* prog, char const* const* argv, char const* const* envp);
+
 #endif // COMMAND_H