Merge pull request rust-lang#588 from jeremyd2019/x86-add-__chkstk

Add __chkstk on i686-pc-windows-gnu.

Author: Amanieu

src/x86.rs

@@ -8,14 +8,27 @@ use core::intrinsics;
 // NOTE These functions are never mangled as they are not tested against compiler-rt
 
 intrinsics! {
+    #[naked]
+    #[cfg(all(
+        windows,
+        target_env = "gnu",
+        not(feature = "no-asm")
+    ))]
+    pub unsafe extern "C" fn __chkstk() {
+        core::arch::asm!(
+            "jmp __alloca", // Jump to __alloca since fallthrough may be unreliable"
+            options(noreturn, att_syntax)
+        );
+    }
+
     #[naked]
     #[cfg(all(
         windows,
         target_env = "gnu",
         not(feature = "no-asm")
     ))]
     pub unsafe extern "C" fn _alloca() {
-        // _chkstk and _alloca are the same function
+        // __chkstk and _alloca are the same function
         core::arch::asm!(
             "push   %ecx",
             "cmp    $0x1000,%eax",