[clang] [ARM] Add __builtin_sponentry like on aarch64

[mstorsjo]

Summary

This is used for calling the SEH aware setjmp on MinGW.

[efriedma]

LGTM

clang/include/clang/Basic/BuiltinsARM.def

 // System registers (ACLE)
 BUILTIN(__builtin_arm_rsr, "UicC*", "nc")
 BUILTIN(__builtin_arm_rsr64, "LLUicC*", "nc")
 BUILTIN(__builtin_arm_rsrp, "v*cC*", "nc")
 BUILTIN(__builtin_arm_wsr, "vcC*Ui", "nc")
 BUILTIN(__builtin_arm_wsr64, "vcC*LLUi", "nc")
 BUILTIN(__builtin_arm_wsrp, "vcC*vC*", "nc")
 
+// Misc
+BUILTIN(__builtin_sponentry, "v*", "c")
+
 // Builtins for implementing ACLE MVE intrinsics. (Unlike NEON, these
 // don't need to live in a separate BuiltinsMVE.def, because they
 // aren't included from both here and BuiltinsAArch64.def.)
 #include "clang/Basic/arm_mve_builtins.inc"
 
 #include "clang/Basic/arm_cde_builtins.inc"
 
 // MSVC

clang/lib/CodeGen/CGBuiltin.cpp

if (BuiltinID == ARM::BI__builtin_arm_rsr ||
     } else {
       ValueType = RegisterType = Int32Ty;
     }
 
     return EmitSpecialRegisterBuiltin(*this, E, RegisterType, ValueType,
                                       AccessKind);
   }
 
+  if (BuiltinID == ARM::BI__builtin_sponentry) {
+    llvm::Function *F = CGM.getIntrinsic(Intrinsic::sponentry, AllocaInt8PtrTy);
+    return Builder.CreateCall(F);
+  }
+
   // Handle MSVC intrinsics before argument evaluation to prevent double
   // evaluation.
   if (Optional<MSVCIntrin> MsvcIntId = translateArmToMsvcIntrin(BuiltinID))
     return EmitMSVCBuiltinExpr(*MsvcIntId, E);
 
   // Deal with MVE builtins
   if (Value *Result = EmitARMMVEBuiltinExpr(BuiltinID, E, ReturnValue, Arch))
     return Result;

clang/test/CodeGen/builtin-sponentry.c

 // RUN: %clang_cc1 -no-opaque-pointers -triple aarch64-windows-gnu -Oz -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -no-opaque-pointers -triple thumbv7-windows-gnu -Oz -emit-llvm %s -o - | FileCheck %s
 
 void *test_sponentry(void) {
   return __builtin_sponentry();
 }
-// CHECK-LABEL: define dso_local i8* @test_sponentry()
+// CHECK-LABEL: define dso_local {{(arm_aapcs_vfpcc )?}}i8* @test_sponentry()
 // CHECK: = tail call i8* @llvm.sponentry.p0i8()
 // CHECK: ret i8*