Don't duplicate references and libraries in MSVC scripts

In order not to duplicate references and libraries in the Visual Studio
project files produced by the MSVC build scripts, have them check if a
particular reference or library already exists before adding the same one
again.

Reviewed-by: Álvaro Herrera, Andrew Dunstan, Dagfinn Ilmari Mannsåker
Discussion: https://postgr.es/m/CAApHDvpo6g5csCTjc_0C7DMvgFPomVb0Rh-AcW5afd=Ya=LRuw@mail.gmail.com

src/tools/msvc/Project.pm

@@ -124,7 +124,10 @@ sub AddReference
 
 	while (my $ref = shift)
 	{
-		push @{ $self->{references} }, $ref;
+		if (! grep { $_ eq $ref} @{ $self->{references} })
+		{
+			push @{ $self->{references} }, $ref;
+		}
 		$self->AddLibrary(
 			"__CFGNAME__/" . $ref->{name} . "/" . $ref->{name} . ".lib");
 	}
@@ -141,7 +144,11 @@ sub AddLibrary
 		$lib = '"' . $lib . """;
 	}
 
-	push @{ $self->{libraries} }, $lib;
+	if (! grep { $_ eq $lib} @{ $self->{libraries} })
+	{
+		push @{ $self->{libraries} }, $lib;
+	}
+
 	if ($dbgsuffix)
 	{
 		push @{ $self->{suffixlib} }, $lib;