Split global_asm! helper macros out from wasmtime-fibers (#4454)

This moves them into a new `wasmtime-asm-macros` crate that can be used not just
from the `wasmtime-fibers` crate but also from other crates (e.g. we will need
them in https://github.com/bytecodealliance/wasmtime/pull/4431).

Cargo.lock

@@ -3339,6 +3339,13 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "wasmtime-asm-macros"
+version = "0.40.0"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "wasmtime-bench-api"
 version = "0.19.0"
@@ -3509,6 +3516,7 @@ dependencies = [
  "cc",
  "cfg-if",
  "rustix",
+ "wasmtime-asm-macros",
  "windows-sys",
 ]