Make simple_global_asm even simpler

Windows builder croaked. This change tries to fix that by actually
calling the global_asm-defined function so the symbol doesn't get
optimized away, if that is in fact what was happening.

Additionally, we provide an empty main() for non-x86 arches.

src/librustc/ich/impls_hir.rs

@@ -881,6 +881,7 @@ fn hash_stable<W: StableHasherResult>(&self,
             hir::ItemFn(..)          |
             hir::ItemMod(..)         |
             hir::ItemForeignMod(..)  |
+            hir::ItemGlobalAsm(..)   |
             hir::ItemTy(..)          |
             hir::ItemEnum(..)        |
             hir::ItemStruct(..)      |
@@ -925,6 +926,7 @@ fn hash_stable<W: StableHasherResult>(&self,
     ItemFn(fn_decl, unsafety, constness, abi, generics, body_id),
     ItemMod(module),
     ItemForeignMod(foreign_mod),
+    ItemGlobalAsm(global_asm),
     ItemTy(ty, generics),
     ItemEnum(enum_def, generics),
     ItemStruct(variant_data, generics),
@@ -1083,6 +1085,7 @@ fn hash_stable<W: StableHasherResult>(&self,
     Upvar(def_id, index, expr_id),
     Label(node_id),
     Macro(def_id, macro_kind),
+    GlobalAsm(def_id),
     Err
 });
 

src/librustc_metadata/schema.rs

@@ -298,6 +298,7 @@ fn hash_stable<W: StableHasherResult>(&self,
             EntryKind::ForeignImmStatic |
             EntryKind::ForeignMutStatic |
             EntryKind::ForeignMod       |
+            EntryKind::GlobalAsm        |
             EntryKind::Field |
             EntryKind::Type => {
                 // Nothing else to hash here.

src/test/run-pass/simple_global_asm.rs

@@ -9,19 +9,21 @@
 // except according to those terms.
 
 #![feature(global_asm)]
+#![feature(naked_functions)]
 
 #[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 global_asm!(r#"
     .global foo
 foo:
-    jmp baz
+    ret
 "#);
 
 extern {
     fn foo();
 }
 
-#[no_mangle]
-pub extern fn baz() {}
+#[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+fn main() { unsafe { foo(); } }
 
+#[cfg(not(any(target_arch = "x86_64", target_arch = "x86")))]
 fn main() {}