[LinkerScript] Refactor KEEP handling in a separate function

[davide]

Summary

This will grow because I have a patch to support:
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
Let's make this a separate function.

[ruiu]

LGTM

ELF/LinkerScript.cpp

 
 private:
   void addFile(StringRef Path);
 
   void readAsNeeded();
   void readEntry();
   void readExtern();
   void readGroup();
+  void readKeep(OutputSectionCommand *Cmd);
   void readInclude();
   void readNothing() {}
   void readOutput();
   void readOutputArch();
   void readOutputFormat();
   void readPhdrs();
   void readSearchDir();
   void readSections();
return StringSwitch<int>(Op)
       .Case(">=", 2)
       .Case("<=", 2)
       .Case("==", 2)
       .Case("!=", 2)
       .Case("&", 1)
       .Default(-1);
 }
 
+void ScriptParser::readKeep(OutputSectionCommand *Cmd) {
+  expect("(");
+  expect("*");
+  expect("(");
+  auto *InCmd = new InputSectionDescription();
+  Cmd->Commands.emplace_back(InCmd);
+  while (!Error && !skip(")")) {
+    Opt.KeptSections.push_back(peek());
+    InCmd->Patterns.push_back(next());
+  }
+  expect(")");
+}
+
 void ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   OutputSectionCommand *Cmd = new OutputSectionCommand(OutSec);
   Opt.Commands.emplace_back(Cmd);
 
   // Read an address expression.
   // https://sourceware.org/binutils/docs/ld/Output-Section-Address.html#Output-Section-Address
   if (peek() != ":")
     Cmd->AddrExpr = readExpr();
while (!Error && !skip("}")) {
     StringRef Tok = next();
     if (Tok == "*") {
       auto *InCmd = new InputSectionDescription();
       Cmd->Commands.emplace_back(InCmd);
       expect("(");
       while (!Error && !skip(")"))
         InCmd->Patterns.push_back(next());
     } else if (Tok == "KEEP") {
-      expect("(");
-      expect("*");
-      expect("(");
-      auto *InCmd = new InputSectionDescription();
-      Cmd->Commands.emplace_back(InCmd);
-      while (!Error && !skip(")")) {
-        Opt.KeptSections.push_back(peek());
-        InCmd->Patterns.push_back(next());
-      }
-      expect(")");
+      readKeep(Cmd);
     } else if (Tok == "PROVIDE") {
       readProvide(false);
     } else if (Tok == "PROVIDE_HIDDEN") {
       readProvide(true);
     } else {
       setError("unknown command " + Tok);
     }
   }