Reland '[lineeditor] Add setHistorySize() method for adjusting history size' (#115442)

Reland: #110092

Buildbot was failing due to an unused variable warning as there were 2
implementations (with and without libedit). Compared to last version,
wrap the variable inside the `#ifdef HAVE_LIBEDIT`.

Apologies for the oversight @vgvassilev

Author: devajithvs

llvm/include/llvm/LineEditor/LineEditor.h

@@ -41,6 +41,7 @@ class LineEditor {
 
   void saveHistory();
   void loadHistory();
+  void setHistorySize(int size);
 
   static std::string getDefaultHistoryPath(StringRef ProgName);
 

llvm/lib/LineEditor/LineEditor.cpp

@@ -17,6 +17,7 @@
 #include <cstdio>
 #ifdef HAVE_LIBEDIT
 #include <histedit.h>
+constexpr int DefaultHistorySize = 800;
 #endif
 
 using namespace llvm;
@@ -220,8 +221,8 @@ LineEditor::LineEditor(StringRef ProgName, StringRef HistoryPath, FILE *In,
            NULL); // Fix the delete key.
   ::el_set(Data->EL, EL_CLIENTDATA, Data.get());
 
+  setHistorySize(DefaultHistorySize);
   HistEvent HE;
-  ::history(Data->Hist, &HE, H_SETSIZE, 800);
   ::history(Data->Hist, &HE, H_SETUNIQUE, 1);
   loadHistory();
 }
@@ -248,6 +249,11 @@ void LineEditor::loadHistory() {
   }
 }
 
+void LineEditor::setHistorySize(int size) {
+  HistEvent HE;
+  ::history(Data->Hist, &HE, H_SETSIZE, size);
+}
+
 std::optional<std::string> LineEditor::readLine() const {
   // Call el_gets to prompt the user and read the user's input.
   int LineLen = 0;
@@ -291,6 +297,7 @@ LineEditor::~LineEditor() {
 
 void LineEditor::saveHistory() {}
 void LineEditor::loadHistory() {}
+void LineEditor::setHistorySize(int size) {}
 
 std::optional<std::string> LineEditor::readLine() const {
   ::fprintf(Data->Out, "%s", Prompt.c_str());