make_makefiles: Avoid duplicate .gitignore entries.

.gitignore

@@ -442,7 +442,6 @@ dlls/rpcrt4/librpcrt4.def
 dlls/rpcrt4/tests/*.ok
 dlls/rpcrt4/tests/rpcrt4_crosstest.exe
 dlls/rpcrt4/tests/server.h
-dlls/rpcrt4/tests/server.h
 dlls/rpcrt4/tests/server_c.c
 dlls/rpcrt4/tests/server_s.c
 dlls/rpcrt4/tests/testlist.c

tools/make_makefiles

@@ -625,11 +625,13 @@ sub update_gitignore(@)
     # prepend a slash to paths that don't have one
     @ignores = map { $_ =~ s/^([^\/]+)$/\/$1/; $_; } @ignores;
 
-    push @ignores, @_;
+    # get rid of duplicates
+    my %ignores = ();
+    foreach my $i (@ignores, @_) { $ignores{$i} = 1; }
 
     replace_in_file( ".gitignore", undef, undef,
                      "# Automatically generated by make_makefiles; DO NOT EDIT!!\n",
-                     join("\n", sort @ignores), "\n" );
+                     join("\n", sort keys %ignores), "\n" );
 }