Global const set loses type

[Mohan-Dhawan]

The below example fails to compile.

module Test;

import spicy;

const bar: set<string> = set("foo");

function is_bar(x: string): bool {
	if ( x in bar )
		return True;
	return False;
}

public type PDU = unit {
	: bytes &eod;

	on %done {
		print is_bar("foo");
	}	
};

The error displayed is

$ spicyc -o test.hlto -j test.spicy 
internal error: unexpected type, want hilti::type::Set but have hilti::type::Auto

--- Aborting
# [0x7ff133d75768] hilti::rt::Backtrace::Backtrace()
# [0x7ff1333e0114] hilti::util::abort_with_backtrace()
# [0x7ff133861438] 
# [0x7ff1338759a4] 
# [0x7ff13387bcca] 
# [0x7ff13387d52f] 
# [0x7ff13387fe75] hilti::detail::ast::coerce(hilti::Node*, hilti::Unit*)
# [0x7ff1338156dd] 
# [0x7ff133815fca] hilti::Unit::resolveAST(hilti::Plugin const&)
# [0x7ff133765561] hilti::Driver::_resolveUnitsWithPlugin(hilti::Plugin const&, std::vector<std::shared_ptr<hilti::Unit>, std::allocator<std::shared_ptr<hilti::Unit> > >, int&)
# [0x7ff133766e2d] hilti::Driver::_resolveUnits()
# [0x7ff1337673bc] hilti::Driver::compileUnits()
# [0x7ff133767a0c] hilti::Driver::compile()
# [0x7ff133768083] hilti::Driver::run()
# [0x557d6660ab3c] main
# [0x7ff1324280d0] 
# [0x7ff132428189] __libc_start_main
# [0x557d6660bec5] _start
Aborted (core dumped)

Changing const to global ensures successful compilation.