Merge topic 'reuse_pch_no_delay' into release-3.18

ef97fbe6c2 PCH: Avoid unnecessary 30s delay on MSBuild Generator with REUSE_FROM

Acked-by: Kitware Robot <[email protected]>
Merge-request: !5102

Source/cmLocalGenerator.cxx

@@ -2789,7 +2789,7 @@ void cmLocalGenerator::CopyPchCompilePdb(
     }
     file << "      break()\n"
          << "    endif()\n";
-    file << "  else()\n"
+    file << "  elseif(NOT EXISTS \"" << from_file << "\")\n"
          << "    execute_process(COMMAND ${CMAKE_COMMAND}"
          << " -E sleep 1)\n"
          << "  endif()\n";