Bug 1737164 - Don't produce symlinks in Windows clang toolchains.

Original patch by Andi-Bogdan Postelnicu <andi@mozilla.com>.

Differential Revision: https://phabricator.services.mozilla.com/D129222

build/build-clang/clang-13-win64.json

@@ -15,6 +15,7 @@
       "bug47258-extract-symbols-mbcs.patch",
       "Remove-FlushViewOfFile-when-unmaping-gcda-files.patch",
       "revert-llvmorg-13-init-7827-g2a078c307204.patch",
-      "loosen-msvc-detection.patch"
+      "loosen-msvc-detection.patch",
+      "win64-no-symlink.patch"
     ]
 }

build/build-clang/win64-no-symlink.patch

@@ -0,0 +1,30 @@
+diff --git a/llvm/cmake/modules/LLVMInstallSymlink.cmake b/llvm/cmake/modules/LLVMInstallSymlink.cmake
+index 3e6a2c9a2648..09fed8085c23 100644
+--- a/llvm/cmake/modules/LLVMInstallSymlink.cmake
++++ b/llvm/cmake/modules/LLVMInstallSymlink.cmake
+@@ -4,17 +4,18 @@
+ 
+ function(install_symlink name target outdir)
+   set(DESTDIR $ENV{DESTDIR})
++  if(CMAKE_HOST_UNIX)
++    set(LINK_OR_COPY create_symlink)
++  else()
++    set(LINK_OR_COPY copy)
++  endif()
++
+   set(bindir "${DESTDIR}${CMAKE_INSTALL_PREFIX}/${outdir}/")
+ 
+   message(STATUS "Creating ${name}")
+ 
+   execute_process(
+-    COMMAND "${CMAKE_COMMAND}" -E create_symlink "${target}" "${name}"
+-    WORKING_DIRECTORY "${bindir}" ERROR_VARIABLE has_err)
+-  if(CMAKE_HOST_WIN32 AND has_err)
+-    execute_process(
+-      COMMAND "${CMAKE_COMMAND}" -E copy "${target}" "${name}"
+-      WORKING_DIRECTORY "${bindir}")
+-  endif()
++    COMMAND "${CMAKE_COMMAND}" -E ${LINK_OR_COPY} "${target}" "${name}"
++    WORKING_DIRECTORY "${bindir}")
+ 
+ endfunction()