Fix build break introduced by https://reviews.llvm.org/D127702

[yinghuitan]

Summary

Fix build break introduced by https://reviews.llvm.org/D127702

lldb/tools/lldb-vscode/BreakpointBase.h

 #include <string>
 #include <vector>
 
 namespace lldb_vscode {
 
 struct BreakpointBase {
   // logMessage part can be either a raw text or an expression.
   struct LogMessagePart {
+    LogMessagePart(llvm::StringRef text, bool is_expr)
+        : text(text), is_expr(is_expr) {}
     llvm::StringRef text;
     bool is_expr;
   };
   // An optional expression for conditional breakpoints.
   std::string condition;
   // An optional expression that controls how many hits of the breakpoint are
   // ignored. The backend is expected to interpret the expression as needed
   std::string hitCondition;

lldb/tools/lldb-vscode/BreakpointBase.cpp

for (const std::pair<int, int> &curly_braces_range :
     size_t expr_len = curly_braces_range.second - curly_braces_range.first - 1;
     logMessageParts.emplace_back(
         llvm::StringRef(logMessage.c_str() + curly_braces_range.first + 1,
                         expr_len),
         /*is_expr=*/true);
     last_raw_text_start = curly_braces_range.second + 1;
   }
   // Trailing raw text after close curly brace.
-  if (logMessage.size() > last_raw_text_start)
+  assert(last_raw_text_start >= 0);
+  if (logMessage.size() > (size_t)last_raw_text_start)
     logMessageParts.emplace_back(
         llvm::StringRef(logMessage.c_str() + last_raw_text_start,
                         logMessage.size() - last_raw_text_start),
         /*is_expr=*/false);
   bp.SetCallback(BreakpointBase::BreakpointHitCallback, this);
 }
 
 /*static*/
 bool BreakpointBase::BreakpointHitCallback(
     void *baton, lldb::SBProcess &process, lldb::SBThread &thread,
     lldb::SBBreakpointLocation &location) {
   if (!baton)
     return true;
 
   BreakpointBase *bp = (BreakpointBase *)baton;
   lldb::SBFrame frame = thread.GetSelectedFrame();
 
   std::string output;
   for (const BreakpointBase::LogMessagePart &messagePart :
        bp->logMessageParts) {
     if (messagePart.is_expr) {
       // Try local frame variables first before fall back to expression
       // evaluation
-      const char *expr = messagePart.text.str().c_str();
+      std::string expr_str = messagePart.text.str();
+      const char *expr = expr_str.c_str();
       lldb::SBValue value =
           frame.GetValueForVariablePath(expr, lldb::eDynamicDontRunTarget);
       if (value.GetError().Fail())
         value = frame.EvaluateExpression(expr);
       const char *expr_val = value.GetValue();
       if (expr_val)
         output += expr_val;
     } else {