[libunwind] [libcxxabi] [libcxx] [libunwind][libcxx][libcxxabi] Fix Exception Handling build for wasm (PR #79667)

[Louis Dionne via cfe-commits]

================
@@ -15,6 +15,7 @@
 
 #include <__libunwind_config.h>
 
+#ifndef __wasm__
----------------
ldionne wrote:

What is the purpose of this header if it's entirely empty on wasm?

https://github.com/llvm/llvm-project/pull/79667