[CodeGen][ARM64EC] Use alias symbol for exporting hybrid_patchable functions.

Exporting $hp_target symbol doesn't make sense, use the unmangled alias instead.
This is not compatible with MSVC, but it makes using dllexport together with
hybrid_patchable attribute possible.

Author: cjacek

llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp

@@ -833,6 +833,11 @@ bool AArch64Arm64ECCallLowering::runOnModule(Module &Mod) {
                                               "EXP+" + MangledName.value())));
       A->setAliasee(&F);
 
+      if (F.hasDLLExportStorageClass()) {
+        A->setDLLStorageClass(GlobalValue::DLLExportStorageClass);
+        F.setDLLStorageClass(GlobalValue::DefaultStorageClass);
+      }
+
       FnsMap[A] = GlobalAlias::create(GlobalValue::LinkOnceODRLinkage,
                                       MangledName.value(), &F);
       PatchableFns.insert(A);

llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll

@@ -238,7 +238,7 @@ define dso_local void @caller() nounwind {
 ; CHECK-NEXT:      .symidx exp
 ; CHECK-NEXT:      .word   0
 ; CHECK-NEXT:      .section        .drectve,"yni"
-; CHECK-NEXT:      .ascii  " /EXPORT:\"#exp$hp_target,EXPORTAS,exp$hp_target\""
+; CHECK-NEXT:      .ascii  " /EXPORT:exp"
 
 ; CHECK-NEXT:      .def    func;
 ; CHECK-NEXT:      .scl    2;