Deps_builder: Win: X64: Fix msys2 setup

on a freshly installed environment diff.exe requires newer runtime
dll's. For now only fix this on X64 as on windows on arm there's
issues with newer msys2 versions (but I do now know exactly what
they are anthony has brought it up in the past) this can however
not remain in a broken state, so fixing it for X64 only.

Also fix typo in download_package function

These two fixes together should bring a fresh vmprep install back
to working order.

build_files/build_environment/cmake/setup_msys2.cmake

@@ -24,7 +24,7 @@ macro(download_package package_name)
   set(MSYS2_${package_name}_FILE ${_final_filename})
   if(NOT EXISTS "${_final_filename}")
     if(MSYS2_USE_UPSTREAM_PACKAGES)
-      set(_final_url ${URI})
+      set(_final_url ${URL})
     else()
       set(_final_url "https://projects.blender.org/blender/lib-windows_x64/media/branch/build_environment/${_file_name}")
     endif()
@@ -132,6 +132,20 @@ if(NOT EXISTS "${DOWNLOAD_DIR}/msys2/msys64/usr/bin/m4.exe")
   )
 
   message(STATUS "Installing required packages")
+  
+  if(NOT BLENDER_PLATFORM_WINDOWS_ARM)
+    # A newer runtime package is required since the tools downloaded in the next step
+    # depend on it, we however cannot update the runtime from a msys2_shell.cmd since
+    # bash.exe will lock the runtime dlls so we execute pacman directly. 
+    #
+    # For now only run this on X64 as there are some known issues (but unknown to me)
+    # with newer msys2 on Windows on ARM. 
+    execute_process(
+      COMMAND ${DOWNLOAD_DIR}/msys2/msys64/usr/bin/pacman -S msys2-runtime --noconfirm 
+      WORKING_DIRECTORY ${DOWNLOAD_DIR}/msys2/msys64
+    )
+  endif()
+  
   execute_process(
     COMMAND ${DOWNLOAD_DIR}/msys2/msys64/msys2_shell.cmd -defterm -no-start -clang64 -c
       "pacman -S patch m4 coreutils pkgconf make diffutils autoconf-wrapper --noconfirm && exit"