Add tests for -Zmiri-check-number-validity

tests/compile-fail/uninit_float.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Zmiri-check-number-validity
+
+// This test is adapted from https://github.com/rust-lang/miri/issues/1340#issue-600900312.
+
+fn main() {
+    let _val = unsafe { std::mem::MaybeUninit::<f32>::uninit().assume_init() };
+    //~^ ERROR type validation failed at .value: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
+}

tests/compile-fail/uninit_integer.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Zmiri-check-number-validity
+
+// This test is from https://github.com/rust-lang/miri/issues/1340#issue-600900312.
+
+fn main() {
+    let _val = unsafe { std::mem::MaybeUninit::<usize>::uninit().assume_init() };
+    //~^ ERROR type validation failed at .value: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
+}

tests/compile-fail/uninit_integer_signed.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Zmiri-check-number-validity
+
+// This test is adapted from https://github.com/rust-lang/miri/issues/1340#issue-600900312.
+
+fn main() {
+    let _val = unsafe { std::mem::MaybeUninit::<i32>::uninit().assume_init() };
+    //~^ ERROR type validation failed at .value: encountered uninitialized bytes, but expected initialized plain (non-pointer) bytes
+}

tests/run-pass/uninit_number_ignored.rs

@@ -0,0 +1,8 @@
+// This test is adapted from https://github.com/rust-lang/miri/issues/1340#issue-600900312.
+// This test passes because -Zmiri-check-number-validity is not passed.
+
+fn main() {
+    let _val1 = unsafe { std::mem::MaybeUninit::<usize>::uninit().assume_init() };
+    let _val2 = unsafe { std::mem::MaybeUninit::<i32>::uninit().assume_init() };
+    let _val3 = unsafe { std::mem::MaybeUninit::<f32>::uninit().assume_init() };
+}