improve doc test for UnsafeCell::raw_get and fix docs error

Author: gftea

library/core/src/cell.rs

@@ -2053,6 +2053,8 @@ impl<T: ?Sized> UnsafeCell<T> {
     ///
     /// let m = MaybeUninit::<UnsafeCell<i32>>::uninit();
     /// unsafe { UnsafeCell::raw_get(m.as_ptr()).write(5); }
+    /// // avoid below which references to uninitialized data
+    /// // unsafe { UnsafeCell::get(&*m.as_ptr()).write(5); }
     /// let uc = unsafe { m.assume_init() };
     ///
     /// assert_eq!(uc.into_inner(), 5);

library/core/src/panic/panic_info.rs

@@ -138,7 +138,7 @@ impl<'a> PanicInfo<'a> {
     /// whose ABI does not support unwinding.
     ///
     /// It is safe for a panic handler to unwind even when this function returns
-    /// true, however this will simply cause the panic handler to be called
+    /// false, however this will simply cause the panic handler to be called
     /// again.
     #[must_use]
     #[unstable(feature = "panic_can_unwind", issue = "92988")]