gccrs: Add new test cases for old issues

#3555, #3591, #3597,
#3651, #3670 & #3672 were all
fixed long ago by some of my older patches, adding test cases to conclude
the issues properly.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3555.rs: New test case.
	* rust/compile/issue-3591.rs: New test case.
	* rust/compile/issue-3597.rs: New test case.
	* rust/compile/issue-3651.rs: New test case.
	* rust/compile/issue-3670.rs: New test case.
	* rust/compile/issue-3672.rs: New test case.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

Author: Polygonalr

gcc/testsuite/rust/compile/issue-3555.rs

@@ -0,0 +1,14 @@
+#![feature(no_core)]
+#![no_core]
+
+fn main() {
+    match SomeStruct(2) {
+        StructConst1(_) => {}
+
+        _ => {}
+    }
+
+    struct SomeStruct(u8);
+
+    const StructConst1: SomeStruct = SomeStruct(1);
+}

gcc/testsuite/rust/compile/issue-3591.rs

@@ -0,0 +1,8 @@
+#![feature(no_core)]
+#![no_core]
+
+fn main() {
+    match (0, 92, 29) {
+        (pat, ..) => {}
+    }
+}

gcc/testsuite/rust/compile/issue-3597.rs

@@ -0,0 +1,11 @@
+#![feature(no_core)]
+#![no_core]
+
+enum E {
+    A = {
+        enum F {  }
+        0
+    }
+}
+
+fn main() {}

gcc/testsuite/rust/compile/issue-3651.rs

@@ -0,0 +1,12 @@
+#![feature(no_core)]
+#![no_core]
+enum E {
+    A = {
+        enum F {
+            Ai32 = -1,
+        }
+        0
+    },
+}
+
+fn main() {}

gcc/testsuite/rust/compile/issue-3670.rs

@@ -0,0 +1,11 @@
+#![feature(no_core)]
+#![no_core]
+enum E {
+    A = {
+        enum Foo {
+            Bar(isize),
+            Baz,
+        }
+        0
+    },
+}

gcc/testsuite/rust/compile/issue-3672.rs

@@ -0,0 +1,12 @@
+// { dg-options "-w" }
+#![feature(no_core)]
+#![no_core]
+struct Y(usize, usize);
+
+fn distinct_variant() {
+    let y = Y(1, 2);
+
+    let a = match y {
+        Y(a, _) => a,
+    };
+}