`PAGESIZE` macro set to garbage value in shared libraries

While experimenting with C++ exception handling support for shared libraries, I discovered that the support for custom page sizes in __macro__PAGESIZE.h (which is only enabled for LLVM v22 and later) is broken for shared libraries, leading to an alignment-related abort() in sbrk when dlmalloc asks for more memory.

I was able to work around this by adding a && !defined __pic__ clause to the preprocessor guard, causing PAGESIZE to be hard-coded to the traditional 0x10000 value when compiling with -fPIC. I'm not sure what the proper way to handle custom page sizes in shared libraries is, but perhaps rather than rely on wasm-ld to define __wasm_first_page_end, it could be imported from env similar to e.g. __heap_end and friends.

Start in __macro__PAGESIZE.h and inspect the preprocessor guard used for LLVM v22 and later, then trace how wasm-ld defines __wasm_first_page_end for shared libraries. Compare that path with the imported __heap_end and related symbols mentioned in the issue. Done means shared-library builds use a valid PAGESIZE and dlmalloc no longer reaches the alignment-related sbrk abort.