patch 9.0.1572: error messages are not translated

Problem:    Error messages are not translated.
Solution:   Add _().
diff --git a/src/os_unix.c b/src/os_unix.c
index 194e4d3..47073ba 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -7705,7 +7705,7 @@
 	    for (i = 0; signal_info[i].sig != -1; i++)
 		if (lc_signal == signal_info[i].sig)
 		    break;
-	    semsg(e_got_sig_str_in_libcall, signal_info[i].name);
+	    semsg(_(e_got_sig_str_in_libcall), signal_info[i].name);
 	}
 #  endif
 # endif