Disable hardening mode

LLVM 18.1.2 adds support for "Hardening Modes" to libcxx
(https://libcxx.llvm.org/Hardening.html). There are four modes: none,
fast, extensive and debug. Different hardening modes make different
trade-offs between the amount of checking and runtime performance. We
for now disable it (i.e., set it to 'none') so that we don't have any
effects on the performance. We can consider enabling it when we ever get
to enable the debug version of libcxx.

Author: aheejin

system/lib/libcxx/include/__config_site

@@ -8,4 +8,5 @@
 #define _LIBCPP_PSTL_CPU_BACKEND_SERIAL
 // __libcpp_verbose_abort creases code size too much
 #define _LIBCPP_AVAILABILITY_HAS_VERBOSE_ABORT 0
+#define _LIBCPP_HARDENING_MODE _LIBCPP_HARDENING_MODE_NONE
 #define _LIBCPP_HAS_NO_TIME_ZONE_DATABASE