[Windows|Arm64|VarArgs] Correctly pass HFA arguments (#18364)

* Fix passing HFA of two floats to vararg methods

Previously, the type would be reported as HFA and enregistered; however,
this is not correct, as arm64 varargs abi requires passing using
int registers.

* Address linux build issue

* Apply final format patch

* Add _TARGET_WINDOWS_

1 files changed, 6 insertions, 5 deletions

diff --git a/src/jit/compiler.hpp b/src/jit/compiler.hpp
index 4e606e6273..f7c7b3d1ac 100644
--- a/src/jit/compiler.hpp
+++ b/src/jit/compiler.hpp
@@ -690,11 +690,12 @@ inline bool isRegParamType(var_types type)
 //    typeSize  - Out param (if non-null) is updated with the size of 'type'.
 //    forReturn - this is true when we asking about a GT_RETURN context;
 //                this is false when we are asking about an argument context
+//    isVarArg  - whether or not this is a vararg fixed arg or variable argument
+//              - if so on arm64 windows getArgTypeForStruct will ignore HFA
+//              - types
 //
-inline bool Compiler::VarTypeIsMultiByteAndCanEnreg(var_types            type,
-                                                    CORINFO_CLASS_HANDLE typeClass,
-                                                    unsigned*            typeSize,
-                                                    bool                 forReturn)
+inline bool Compiler::VarTypeIsMultiByteAndCanEnreg(
+    var_types type, CORINFO_CLASS_HANDLE typeClass, unsigned* typeSize, bool forReturn, bool isVarArg)
 {
     bool     result = false;
     unsigned size   = 0;
@@ -710,7 +711,7 @@ inline bool Compiler::VarTypeIsMultiByteAndCanEnreg(var_types            type,
         else
         {
             structPassingKind howToPassStruct;
-            type = getArgTypeForStruct(typeClass, &howToPassStruct, size);
+            type = getArgTypeForStruct(typeClass, &howToPassStruct, isVarArg, size);
         }
         if (type != TYP_UNKNOWN)
         {