sim: 16-byte align CSimContext on x86_64-pc-windows-gnu

The C `jmp_buf` embedded in this FFI struct needs 16-byte alignment under
mingw's setjmp (saves XMM registers with movaps). The C compiler aligns
the struct to 16 to satisfy that, but Rust's repr(C) only picked the
8-byte alignment of [u64; 48], so the field could land 8-byte aligned and
setjmp faulted with STATUS_ACCESS_VIOLATION.

Signed-off-by: José Simões <jose.simoes@eclo.solutions>

Author: josesimoes

sim/mcuboot-sys/src/api.rs

@@ -89,7 +89,12 @@ impl Default for FlashContext {
     }
 }
 
-#[repr(C)]
+// The C side embeds a `jmp_buf` here. On x86_64-pc-windows-gnu mingw's `_setjmpex` saves XMM
+// registers with `movaps`, which requires 16-byte alignment; the C compiler therefore aligns
+// this struct to 16 to satisfy that. Match that on the Rust side or the FFI struct ends up
+// only 8-byte aligned and setjmp faults with STATUS_ACCESS_VIOLATION.
+#[cfg_attr(all(target_os = "windows", target_env = "gnu"), repr(C, align(16)))]
+#[cfg_attr(not(all(target_os = "windows", target_env = "gnu")), repr(C))]
 #[derive(Debug)]
 pub struct CSimContext {
     pub flash_counter: libc::c_int,