On emscripten, some implementations in os-posix.c can't be used such as
daemonizing and changing user. This commit introduces os-wasm.c and
os-wasm.h which are forked from os-posix.c and os-posix.h and patched for
targetting Emscripten.
Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
Link: https://lore.kernel.org/r/9fc7b106ecf86675b4532bd6778b7b5945442f89.1745820062.git.ktokunaga.mail@gmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
