Make pg_trgm tests independ from standard_conforming_string. Tests uses

regular expression which contains backslash.

contrib/pg_trgm/expected/pg_trgm.out

@@ -7,6 +7,9 @@ WHERE opc.oid >= 16384 AND NOT amvalidate(opc.oid);
 --------+---------
 (0 rows)
 
+--backslash is used in tests below, installcheck will fail if
+--standard_conforming_string is off
+set standard_conforming_strings=on;
 select show_trgm('');
  show_trgm 
 -----------

contrib/pg_trgm/sql/pg_trgm.sql

@@ -5,6 +5,10 @@ SELECT amname, opcname
 FROM pg_opclass opc LEFT JOIN pg_am am ON am.oid = opcmethod
 WHERE opc.oid >= 16384 AND NOT amvalidate(opc.oid);
 
+--backslash is used in tests below, installcheck will fail if
+--standard_conforming_string is off
+set standard_conforming_strings=on;
+
 select show_trgm('');
 select show_trgm('(*&^$@%@');
 select show_trgm('a b c');