lld: Handle parsing AT(ADDR(.foo-bar)).

The problem we had with it is that anything inside an AT is an
expression, so we failed to parse the section name because of the - in
it.

Requested by:	royger
Obtained from:	LLVM r322801 by Rafael Espindola

contrib/llvm/tools/lld/ELF/ScriptParser.cpp

@@ -930,7 +930,10 @@ ByteCommand *ScriptParser::readByteCommand(StringRef Tok) {
 
 StringRef ScriptParser::readParenLiteral() {
   expect("(");
+  bool Orig = InExpr;
+  InExpr = false;
   StringRef Tok = next();
+  InExpr = Orig;
   expect(")");
   return Tok;
 }