Adjust backslash alignment syntax-check

We have a check for backslash alignment that checks for two blanks preceding a
backslash.  However there can be alignment done using a tabulator and in some
cases one might be enough.  There are none currently, but I found out that was
the case before. at some point.  so let's check for \t preceding the final
backslash as well.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

cfg.mk

@@ -1038,7 +1038,7 @@ sc_prohibit_http_urls:
 	  $(_sc_search_regexp)
 
 sc_prohibit_backslash_alignment:
-	@prohibit='[[:blank:]][[:blank:]]\\$$' \
+	@prohibit='([[:blank:]][[:blank:]]|	)\\$$' \
 	in_vc_files='*\.([chx]|am|mk)$$' \
 	halt='Do not attempt to right-align backslashes' \
 	  $(_sc_search_regexp)