unlit: replace the SHEBANG with an empty line

This corrects the line numbers for literate code after a shebang.
Fixes #13414.

Test Plan: validate

Reviewers: austin, bgamari, trofi

Reviewed By: bgamari, trofi

Subscribers: trofi, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3333

testsuite/tests/parser/should_fail/T13414.lhs

+#!/usr/bin/env runhaskell
+> module T13414 where
+> main = invalid_ident_

testsuite/tests/parser/should_fail/T13414.stderr

+
+T13414.lhs:3:10: error: Variable not in scope: invalid_ident_

testsuite/tests/parser/should_fail/all.T

@@ -97,3 +97,4 @@ test('T12051', normal, compile_fail, [''])
 test('T12429', normal, compile_fail, [''])
 test('T12811', normal, compile_fail, [''])
 test('T13260', normal, compile_fail, [''])
+test('T13414', literate, compile_fail, [''])

utils/unlit/unlit.c

@@ -296,6 +296,9 @@ static void unlit(char *file, FILE *istream, FILE *ostream)
 	    }
 	}
 #endif
+	if (this == SHEBANG) {
+	    myputc('\n', ostream);
+	}
     } while(this!=ENDFILE);
 
     if (defnsread==0)