Add `@main` to Runic module

This now supports the `-m` and the `juliac` workflow.

juliac/runicc.jl

@@ -1,7 +1,7 @@
 using Runic: Runic
 
 # Compileable main function corresponding to `int main(int argc, char** argv)`
-function @main(args::Vector{String})::Cint
+function (@main)(args::Vector{String})::Cint
     if length(args) == 1
         Runic.print_help()
         return 0

src/Runic.jl

@@ -2,6 +2,10 @@
 
 module Runic
 
+function (@main)(argv)
+    return main(argv)
+end
+
 if VERSION >= v"1.11.0-DEV.469"
     let str = "public format_file, format_string"
         eval(Meta.parse(str))