[BOLT] Update section index for symbols from unemitted functions

Summary:
Under some conditions, e.g. while running in lite mode or when a
function is non-simple, BOLT may decide not to emit function code and
hence there's no need to update the symbol. However, since we change
section table, the corresponding section index may need an update.

Also, update section index for ICF symbols.

(cherry picked from FBD21970017)

bolt/src/RewriteInstance.cpp

@@ -3633,6 +3633,7 @@ void RewriteInstance::updateELFSymbolTable(
                         .toStringRef(Buf));
       ICFSymbol.st_value = ICFParent->getOutputAddress();
       ICFSymbol.st_size = ICFParent->getOutputSize();
+      ICFSymbol.st_shndx = ICFParent->getCodeSection()->getIndex();
       Symbols.emplace_back(ICFSymbol);
     }
     if (Function.isSplit() && Function.cold().getAddress()) {
@@ -3735,12 +3736,14 @@ void RewriteInstance::updateELFSymbolTable(
     auto NewSymbol = Symbol;
 
     if (Function) {
-      // If the symbol matched a function that was not emitted, leave the
-      // symbol unchanged.
+      // If the symbol matched a function that was not emitted, update the
+      // corresponding section index but otherwise leave it unchanged.
       if (Function->isEmitted()) {
         NewSymbol.st_value = Function->getOutputAddress();
         NewSymbol.st_size = Function->getOutputSize();
         NewSymbol.st_shndx = Function->getCodeSection()->getIndex();
+      } else if (Symbol.st_shndx < ELF::SHN_LORESERVE) {
+        NewSymbol.st_shndx = NewSectionIndex[Symbol.st_shndx];
       }
 
       // Add new symbols to the symbol table if necessary.