Fix Runic.main on old Julia versions.

src/Runic.jl

@@ -461,9 +461,6 @@ function format_file(inputfile::AbstractString, outputfile::AbstractString = inp
 end
 
 include("runestone.jl")
-
-if isdefined(Base, Symbol("@main"))
 include("main.jl")
-end
 
 end # module

src/main.jl

@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: MIT
 
+@static if VERSION >= v"1.8"
     errno::Cint = 0
+else
+    errno = 0
+end
 
 function panic(msg...)
     printstyled(stderr, "ERROR: "; color = :red, bold = true)
@@ -16,7 +20,7 @@ function panic(msg...)
     return errno
 end
 
-function (@main)(argv)
+function main(argv)
     # Reset errno
     global errno = 0
 
@@ -146,3 +150,7 @@ function (@main)(argv)
 
     return errno
 end
+
+@static if isdefined(Base, Symbol("@main"))
+    @main
+end