llvmPackages_5.compiler-rt: fix build against gcc-12
[ 11%] Building CXX object lib/xray/CMakeFiles/clang_rt.xray-x86_64.dir/xray_buffer_queue.cc.o
In file included from lib/xray/xray_buffer_queue.cc:15:
lib/xray/xray_buffer_queue.h:35:5: error: 'size_t' does not name a type
35 | size_t Size = 0;
| ^~~~~~
lib/xray/xray_buffer_queue.h:23:1: note: 'size_t' is defined in header '<cstddef>';
did you forget to '#include <cstddef>'?
22 | #include <utility>
+++ |+#include <cstddef>
23 |