Set target_family="wasm" for wasm targets

compiler/rustc_target/src/spec/mod.rs

@@ -1046,7 +1046,7 @@ pub struct TargetOptions {
     ///
     /// Common options are: "unix", "windows". Defaults to no families.
     ///
-    /// See https://doc.rust-lang.org/reference/conditional-compilation.html#target_family
+    /// See <https://doc.rust-lang.org/reference/conditional-compilation.html#target_family>.
     pub families: Vec<String>,
     /// Whether the target toolchain's ABI supports returning small structs as an integer.
     pub abi_return_struct_as_int: bool,

compiler/rustc_target/src/spec/wasm_base.rs

@@ -61,6 +61,7 @@ pub fn options() -> TargetOptions {
 
     TargetOptions {
         is_like_wasm: true,
+        families: vec!["wasm".to_string()],
 
         // we allow dynamic linking, but only cdylibs. Basically we allow a
         // final library artifact that exports some symbols (a wasm module) but