[ELF] Copy IsPreemptible in replaceSymbol()

[MaskRay]

Summary

Otherwise, we may set IsPreemptible (e.g. --dynamic-list) then clear it
(in replaceCommonSymbols()).

[ruiu]

LGTM

ELF/Symbols.h

inline void replaceSymbol(Symbol *Sym, const Symbol &New) {
   memcpy(Sym, &New, getSymbolSize(New));
 
   Sym->VersionId = Old.VersionId;
   Sym->Visibility = Old.Visibility;
   Sym->IsUsedInRegularObj = Old.IsUsedInRegularObj;
   Sym->ExportDynamic = Old.ExportDynamic;
   Sym->CanInline = Old.CanInline;
   Sym->Traced = Old.Traced;
+  Sym->IsPreemptible = Old.IsPreemptible;
   Sym->ScriptDefined = Old.ScriptDefined;
 
   // Print out a log message if --trace-symbol was specified.
   // This is for debugging.
   if (Sym->Traced)
     printTraceSymbol(Sym);
 }
 
 void maybeWarnUnorderableSymbol(const Symbol *Sym);
 } // namespace elf
 } // namespace lld
 
 #endif

test/ELF/dynamic-list-preempt-replace-symbol.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
+# RUN: echo '{ common; };' > %t.list
+# RUN: ld.lld --dynamic-list %t.list -shared %t.o -o %t.so
+
+# RUN: llvm-readobj -r %t.so | FileCheck %s
+
+# CHECK: R_X86_64_GLOB_DAT common 0x0
+
+movq common@gotpcrel(%rip), %rax
+
+.type common,@object
+.comm common,4,4