[llvm-lib] Use ARM64EC machine type for import libraries when -machine:arm64x is used.

This is compatible with MSVC, -machine:arm64x is essentially an alias to -machine:arm64ec.
To make a type library that exposes both native and EC symbols, an additional
-defArm64Native argument is needed in both cases.

Author: cjacek

llvm/lib/Object/COFFImportFile.cpp

@@ -626,8 +626,11 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
                          MachineTypes Machine, bool MinGW,
                          ArrayRef<COFFShortExport> NativeExports) {
 
-  MachineTypes NativeMachine =
-      isArm64EC(Machine) ? IMAGE_FILE_MACHINE_ARM64 : Machine;
+  MachineTypes NativeMachine = Machine;
+  if (isArm64EC(Machine)) {
+    NativeMachine = IMAGE_FILE_MACHINE_ARM64;
+    Machine = IMAGE_FILE_MACHINE_ARM64EC;
+  }
 
   std::vector<NewArchiveMember> Members;
   ObjectFactory OF(llvm::sys::path::filename(ImportName), NativeMachine);

llvm/test/tools/llvm-lib/arm64ec-implib.test

@@ -96,6 +96,11 @@ READOBJ-NEXT: Name type: name
 READOBJ-NEXT: Export name: dataexp
 READOBJ-NEXT: Symbol: __imp_dataexp
 
+Using -machine:arm64x gives the same output.
+RUN: llvm-lib -machine:arm64x -def:test.def -out:test.lib
+RUN: llvm-nm --print-armap test.lib | FileCheck -check-prefix=ARMAP %s
+RUN: llvm-readobj test.lib | FileCheck -check-prefix=READOBJ %s
+
 Creating a new lib containing the existing lib:
 RUN: llvm-lib -machine:arm64ec test.lib -out:test2.lib
 RUN: llvm-nm --print-armap test2.lib | FileCheck -check-prefix=ARMAP %s
@@ -246,7 +251,9 @@ READOBJX-NEXT: Symbol: __imp_dataexp
 
 
 RUN: llvm-lib -machine:arm64ec -def:test.def -defArm64Native:test2.def -out:test2.lib
+RUN: llvm-lib -machine:arm64ec -def:test.def -defArm64Native:test2.def -out:test2x.lib
 RUN: llvm-nm --print-armap test2.lib | FileCheck -check-prefix=ARMAPX2 %s
+RUN: llvm-nm --print-armap test2x.lib | FileCheck -check-prefix=ARMAPX2 %s
 
 ARMAPX2:      Archive map
 ARMAPX2-NEXT: __IMPORT_DESCRIPTOR_test2 in test2.dll