[LLD][COFF] Use getMachineArchType in LinkerDriver::getArch. (#87499)

Adds support for ARM64EC, which should use the same search paths as
ARM64.

It's similar to #87370 and #87495. The test is based on the existing x86
test. Generally ARM64EC libraries are shipped together with native ARM64
libraries (using ECSYMBOLS section mechanism).

getMachineArchType uses Triple::thumb, while the existing
implementation uses Triple::arm. It's ultimately passed to
MSVCPaths.cpp functions, so modify them to accept both forms.

Author: cjacek

lld/COFF/Driver.cpp

@@ -157,18 +157,7 @@ StringRef LinkerDriver::mangle(StringRef sym) {
 }
 
 llvm::Triple::ArchType LinkerDriver::getArch() {
-  switch (ctx.config.machine) {
-  case I386:
-    return llvm::Triple::ArchType::x86;
-  case AMD64:
-    return llvm::Triple::ArchType::x86_64;
-  case ARMNT:
-    return llvm::Triple::ArchType::arm;
-  case ARM64:
-    return llvm::Triple::ArchType::aarch64;
-  default:
-    return llvm::Triple::ArchType::UnknownArch;
-  }
+  return getMachineArchType(ctx.config.machine);
 }
 
 bool LinkerDriver::findUnderscoreMangle(StringRef sym) {

lld/test/COFF/print-search-paths-arm64.s

@@ -0,0 +1,24 @@
+# REQUIRES: aarch64
+
+# RUN: llvm-mc -triple aarch64-windows-msvc %s -filetype=obj -o %t.aarch64.obj
+# RUN: lld-link -dll -noentry -winsysroot:%t.dir/sysroot -vctoolsversion:1.1.1.1 -winsdkversion:10.0.1 -libpath:custom-dir \
+# RUN:           %t.aarch64.obj -print-search-paths | FileCheck -DSYSROOT=%t.dir %s
+
+# RUN: llvm-mc -triple arm64ec-windows-msvc %s -filetype=obj -o %t.arm64ec.obj
+# RUN: lld-link -dll -noentry -winsysroot:%t.dir/sysroot -vctoolsversion:1.1.1.1 -winsdkversion:10.0.1 -libpath:custom-dir \
+# RUN:           %t.arm64ec.obj -print-search-paths -machine:arm64ec | FileCheck -DSYSROOT=%t.dir %s
+
+# CHECK: Library search paths:
+# CHECK-NEXT:   (cwd)
+# CHECK-NEXT:   custom-dir
+# CHECK-NEXT:   [[CPATH:.*]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib{{[/\\]}}windows
+# CHECK-NEXT:   [[CPATH]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib
+# CHECK-NEXT:   [[CPATH]]lib
+# CHECK-NEXT:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}DIA SDK{{[/\\]}}lib{{[/\\]}}arm64
+# CHECK-NEXT:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}lib{{[/\\]}}arm64
+# CHECK-NEXT:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}atlmfc{{[/\\]}}lib{{[/\\]}}arm64
+# CHECK-NEXT:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}Windows Kits{{[/\\]}}10{{[/\\]}}Lib{{[/\\]}}10.0.1{{[/\\]}}ucrt{{[/\\]}}arm64
+# CHECK-NEXT:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}Windows Kits{{[/\\]}}10{{[/\\]}}Lib{{[/\\]}}10.0.1{{[/\\]}}um{{[/\\]}}arm64
+
+        .data
+        .word 1

llvm/lib/WindowsDriver/MSVCPaths.cpp

@@ -268,6 +268,7 @@ const char *archToWindowsSDKArch(Triple::ArchType Arch) {
   case Triple::ArchType::x86_64:
     return "x64";
   case Triple::ArchType::arm:
+  case Triple::ArchType::thumb:
     return "arm";
   case Triple::ArchType::aarch64:
     return "arm64";
@@ -285,6 +286,7 @@ const char *archToLegacyVCArch(Triple::ArchType Arch) {
   case Triple::ArchType::x86_64:
     return "amd64";
   case Triple::ArchType::arm:
+  case Triple::ArchType::thumb:
     return "arm";
   case Triple::ArchType::aarch64:
     return "arm64";
@@ -300,6 +302,7 @@ const char *archToDevDivInternalArch(Triple::ArchType Arch) {
   case Triple::ArchType::x86_64:
     return "amd64";
   case Triple::ArchType::arm:
+  case Triple::ArchType::thumb:
     return "arm";
   case Triple::ArchType::aarch64:
     return "arm64";
@@ -321,6 +324,7 @@ bool appendArchToWindowsSDKLibPath(int SDKMajor, SmallString<128> LibPath,
       sys::path::append(LibPath, "x64");
       break;
     case Triple::arm:
+    case Triple::thumb:
       // It is not necessary to link against Windows SDK 7.x when targeting ARM.
       return false;
     default: