[llvm-profgen] Ignore inline frames with an emtpy function name (llvm#66678)

Broken debug information can give empty names for an inlined frame, e.g,
```

0x1d605c68: ryKeyINS7_17SmartCounterTypesEEESt10shared_ptrINS7_15AsyncCacheValueIS9_EEESaIhESt6atomicEEE9fetch_subElSt12memory_order at   Filename: edata.h
  Function start filename: edata.h
  Function start line: 266
  Function start address: 0x1d605c68
  Line: 267
  Column: 0
 (inlined by)  at   Filename: edata.h
  Function start filename: edata.h
  Function start line: 274
  Function start address: 0x1d605c68
  Line: 275
  Column: 0
 (inlined by) _EEEmmEv at   Filename: arena.c
  Function start filename: arena.c
  Function start line: 1303
  Line: 1308
  Column: 0
```

This patch avoids creating a sample context with an empty function name
by stopping tracking at that frame. This prevents a hash failure that
leads to an ICE, where empty context serves at an empty key for the
underlying MapVector
https://github.com/llvm/llvm-project/blob/7624de5beae2f142abfdb3e32a63c263a586d768/llvm/lib/ProfileData/SampleProfWriter.cpp#L261

Author: htyu

llvm/include/llvm/ProfileData/SampleProf.h

@@ -533,7 +533,9 @@ class SampleContext {
   SampleContext() : State(UnknownContext), Attributes(ContextNone) {}
 
   SampleContext(StringRef Name)
-      : Name(Name), State(UnknownContext), Attributes(ContextNone) {}
+      : Name(Name), State(UnknownContext), Attributes(ContextNone) {
+        assert(!Name.empty() && "Name is empty");
+      }
 
   SampleContext(SampleContextFrames Context,
                 ContextStateMask CState = RawContext)

llvm/tools/llvm-profgen/ProfiledBinary.cpp

@@ -865,7 +865,7 @@ SampleContextFrameVector ProfiledBinary::symbolize(const InstructionPointer &IP,
   SampleContextFrameVector CallStack;
   for (int32_t I = InlineStack.getNumberOfFrames() - 1; I >= 0; I--) {
     const auto &CallerFrame = InlineStack.getFrame(I);
-    if (CallerFrame.FunctionName == "<invalid>")
+    if (CallerFrame.FunctionName.empty() || (CallerFrame.FunctionName == "<invalid>"))
       break;
 
     StringRef FunctionName(CallerFrame.FunctionName);