Execs: Postprocess native dynamic binaries with C code

- Part of Lua code (sb_execve_postprocess_native_executable()
  in argvenvp.lua) was implemented in C (=> added new file
  execs/exec_postprocess.c)

execs/Makefile

@@ -4,6 +4,7 @@ objs := $(D)/exec_ruletree_maint.o \
 	$(D)/exec_policy_selection.o \
 	$(D)/exec_map_script_interp.o \
 	$(D)/exec_policy_ruletree.o \
+	$(D)/exec_postprocess.o \
 	$(D)/sb_exec.o
 
 $(D)/sb_exec.o: preload/exported.h

execs/exec_policy_ruletree.c

@@ -50,8 +50,13 @@ const char *exec_policy_get_string(exec_policy_handle_t eph,
 		offs = ruletree_catalog_find_value_from_catalog(
 			eph.exec_policy_offset, s_name);
 		str = offset_to_ruletree_string_ptr(offs, NULL);
-                SB_LOG(SB_LOGLEVEL_NOISE,
-                        "%s: %s='%s'", __func__, s_name, str, fldoffs);
+		if (str) {
+			SB_LOG(SB_LOGLEVEL_NOISE,
+				"%s: %s='%s'", __func__, s_name, str, fldoffs);
+		} else {
+			SB_LOG(SB_LOGLEVEL_NOISE,
+				"%s: No %s", __func__, s_name, fldoffs);
+		}
                 return(str);
 	}
 	return(NULL);