[memprof] Remove const from the return type of toMemProfRecord (#93415)

"const" being removed in this patch prevents the move semantics from
being used in:

  AI.CallStack = Callback(IndexedAI.CSId);

With this patch on an indexed MemProf Version 2 profile, the cycle
count and instruction count go down by 13.3% and 26.3%, respectively,
with "llvm-profdata show" modified to deserialize all MemProfRecords.

Author: kazutakahirata

llvm/include/llvm/ProfileData/MemProf.h

@@ -426,8 +426,8 @@ struct IndexedMemProfRecord {
   // Convert IndexedMemProfRecord to MemProfRecord.  Callback is used to
   // translate CallStackId to call stacks with frames inline.
   MemProfRecord toMemProfRecord(
-      llvm::function_ref<const llvm::SmallVector<Frame>(const CallStackId)>
-          Callback) const;
+      llvm::function_ref<llvm::SmallVector<Frame>(const CallStackId)> Callback)
+      const;
 
   // Returns the GUID for the function name after canonicalization. For
   // memprof, we remove any .llvm suffix added by LTO. MemProfRecords are

llvm/lib/ProfileData/MemProf.cpp

@@ -245,8 +245,8 @@ IndexedMemProfRecord::deserialize(const MemProfSchema &Schema,
 }
 
 MemProfRecord IndexedMemProfRecord::toMemProfRecord(
-    llvm::function_ref<const llvm::SmallVector<Frame>(const CallStackId)>
-        Callback) const {
+    llvm::function_ref<llvm::SmallVector<Frame>(const CallStackId)> Callback)
+    const {
   MemProfRecord Record;
 
   Record.AllocSites.reserve(AllocSites.size());