Fix runtime crash for setjmp in Windows related to an hidden second argument not normally accessible needing to be set to 0.

core/c/libc/setjmp.odin

@@ -8,8 +8,23 @@ when ODIN_OS == "windows" {
 	foreign import libc "system:c"
 }
 
-@(default_calling_convention="c")
+when ODIN_OS == "windows" {
-foreign libc {
+	@(default_calling_convention="c")
+	foreign libc {
+		// 7.13.1 Save calling environment
+		//
+		// NOTE(dweiler): C11 requires setjmp be a macro, which means it won't
+		// necessarily export a symbol named setjmp but rather _setjmp in the case
+		// of musl, glibc, BSD libc, and msvcrt.
+		//
+		// TODO(mv): Some description of the extra argument, and maybe a link describing
+		// it in more detail?
+		@(link_name="_setjmp")
+		setjmp  :: proc(env: ^jmp_buf, hack: rawptr = nil) -> int ---;
+	}
+} else {
+	@(default_calling_convention="c")
+	foreign libc {
 		// 7.13.1 Save calling environment
 		//
 		// NOTE(dweiler): C11 requires setjmp be a macro, which means it won't
@@ -17,7 +32,11 @@ foreign libc {
 		// of musl, glibc, BSD libc, and msvcrt.
 		@(link_name="_setjmp")
 		setjmp  :: proc(env: ^jmp_buf) -> int ---;
+	}
+}
 
+@(default_calling_convention="c")
+foreign libc {
 	// 7.13.2 Restore calling environment
 	longjmp :: proc(env: ^jmp_buf, val: int) -> ! ---;
 }