Exclude setjmp runtime from LTO (#529)

This fixes errors like:
```
wasm-ld: error: /Volumes/PortableSSD/git/wasi-sdk/build/install/bin/../share/wasi-sysroot/lib/wasm32-wasi/llvm-lto/19.1.0-wasi-sdk/libsetjmp.a(rt.o): attempt to add bitcode file after LTO (__wasm_longjmp)
```

Note: Any symbol that the compiler might generate at bitcode compile
time either need to be unconditionally included at LTO time, or not
built as LTO. This is because LTO object files cannot be added to the
link after LTO time.

Author: yamt

Makefile

@@ -264,6 +264,7 @@ LIBC_TOP_HALF_MUSL_SOURCES = \
 LIBC_NONLTO_SOURCES = \
     $(addprefix $(LIBC_TOP_HALF_MUSL_SRC_DIR)/, \
         exit/atexit.c \
+        setjmp/wasm32/rt.c \
     )
 
 ifeq ($(WASI_SNAPSHOT), p2)