Define more variables in __config_site

libcxx decides to almost all configuration macros to be defined. So
before it tested whether a macro was defined/undefined, and now it
assumes it is defined and tests whether its value is 1/0.

Before llvm/llvm-project#112094
`_config_site.in` used to use `#cmakedefine`, which only defined
variables when they were enabled, but now it uses `#cmakedefine01`,
which always defines variables and assigns 1 or 0 depending on whether
the feature is enabled.

So this change adds `#define` to each variable that `_config_site.in`
has an entry of. The value assigned is 1 if it was defined in our
previous Emscripten environment and 0 if not.

Author: aheejin

system/lib/libcxx/include/__config_site

@@ -1,10 +1,27 @@
 // Set the LIBCPP ABI version 2 under emscripten so that we get nicely aligned string
 // data and other nice fixes.
 #define _LIBCPP_ABI_VERSION 2
-#define _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS
-#define _LIBCPP_HAS_MUSL_LIBC
 #define _LIBCPP_ABI_NAMESPACE __2
-// Emscripten doesn't use PSTL at the moment.
+#define _LIBCPP_ABI_FORCE_ITANIUM 0
+#define _LIBCPP_ABI_FORCE_MICROSOFT 0
+#define _LIBCPP_HAS_THREADS 1
+#define _LIBCPP_HAS_MONOTONIC_CLOCK 1
+#define _LIBCPP_HAS_MUSL_LIBC 1
+#define _LIBCPP_HAS_THREAD_API_PTHREAD 1
+#define _LIBCPP_HAS_THREAD_API_EXTERNAL 0
+#define _LIBCPP_HAS_THREAD_API_WIN32 0
+#define _LIBCPP_HAS_THREAD_API_C11 0
+#define _LIBCPP_HAS_VENDOR_AVAILABILITY_ANNOTATIONS 0
+#define _LIBCPP_HAS_FILESYSTEM 1
+#define _LIBCPP_HAS_RANDOM_DEVICE 1
+#define _LIBCPP_HAS_LOCALIZATION 1
+#define _LIBCPP_HAS_UNICODE 1
+#define _LIBCPP_HAS_WIDE_CHARACTERS 1
+#define _LIBCPP_HAS_TIME_ZONE_DATABASE 0
+#define _LIBCPP_INSTRUMENTED_WITH_ASAN 0
+
+// PSTL backends: Emscripten doesn't use PSTL at the moment.
 #define _LIBCPP_PSTL_BACKEND_SERIAL
+
+// Hardening
 #define _LIBCPP_HARDENING_MODE_DEFAULT _LIBCPP_HARDENING_MODE_NONE
-#define _LIBCPP_HAS_NO_TIME_ZONE_DATABASE