Disable backtrace tests on i686-pc-windows-gnu since it's broken by FPO

src/test/run-pass/backtrace-debuginfo.rs

@@ -37,6 +37,7 @@
                     target_os = "ios",
                     target_os = "android",
                     all(target_os = "linux", target_arch = "arm"),
+                    all(target_os = "windows", target_pointer_width = "32"),
                     target_os = "freebsd",
                     target_os = "dragonfly",
                     target_os = "bitrig",

src/test/run-pass/backtrace.rs

@@ -104,6 +104,10 @@ fn runtest(me: &str) {
 }
 
 fn main() {
+    if cfg!(windows) && cfg!(target_env = "gnu") && cfg!(target_pointer_width = "32") {
+        return
+    }
+
     let args: Vec<String> = env::args().collect();
     if args.len() >= 2 && args[1] == "fail" {
         foo();