[WebAssembly] Allow absolute symbols in the linking section (symbol table) (#67493)

Fixes a crash in `-Wl,-emit-relocs` where the linker was not able to
write linker-synthetic absolute symbols to the symbol table.

This change adds a new symbol flag (`WASM_SYMBOL_ABS`), which means that
the symbol's offset is absolute and not relative to a given segment.
Such symbols include `__stack_low` and `__stack_low`.

Note that wasm object files never contains such symbols, only binaries
linked with `-Wl,-emit-relocs`.

Fixes: #67111