Two test cases where Rust calls C using enums by value

One calls into C functions passing non-c-like enumerations by
value. The other calls into C expecting non-C-like enumerations as
returns.

These test cases are based on the tests provided by @bitwalker on
issue #68190. The original tests were provided at:
2688d5c672

src/test/run-make-fulldeps/pass-non-c-like-enum-to-c/Makefile

@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all:
+	$(CC) -c test.c -o $(call STATICLIB,test) $(EXTRACFLAGS) $(EXTRACXXFLAGS)
+	$(RUSTC) nonclike.rs -L$(TMPDIR) -ltest
+	$(call RUN,nonclike)

src/test/run-make-fulldeps/pass-non-c-like-enum-to-c/nonclike.rs

@@ -0,0 +1,24 @@
+#![crate_type = "bin"]
+#![crate_name = "nonclike"]
+
+#[repr(C, u8)]
+pub enum TT {
+    AA(u64, u64),
+    BB,
+}
+
+#[repr(C,u8)]
+pub enum T {
+    A(u64),
+    B,
+}
+
+extern "C" {
+    pub fn t_add(a: T, b: T) -> u64;
+    pub fn tt_add(a: TT, b: TT) -> u64;
+}
+
+fn main() {
+    assert_eq!(33, unsafe { tt_add(TT::AA(1,2), TT::AA(10,20)) });
+    assert_eq!(11, unsafe { t_add(T::A(1), T::A(10)) });
+}

src/test/run-make-fulldeps/pass-non-c-like-enum-to-c/test.c

@@ -0,0 +1,85 @@
+#include <stdint.h>
+
+/* This is the code generated by cbindgen 0.12.1 for the `enum TT`
+ * type in nonclike.rs . */
+enum TT_Tag {
+  AA,
+  BB,
+};
+typedef uint8_t TT_Tag;
+
+typedef struct {
+  uint64_t _0;
+  uint64_t _1;
+} AA_Body;
+
+typedef struct {
+  TT_Tag tag;
+  union {
+    AA_Body aa;
+  };
+} TT;
+
+/* This is the code generated by cbindgen 0.12.1 for the `enum T` type
+ * in nonclike.rs . */
+enum T_Tag {
+  A,
+  B,
+};
+typedef uint8_t T_Tag;
+
+typedef struct {
+  uint64_t _0;
+} A_Body;
+
+typedef struct {
+  T_Tag tag;
+  union {
+    A_Body a;
+  };
+} T;
+
+uint64_t tt_add(TT a, TT b) {
+  if (a.tag == AA && b.tag == AA) {
+    return a.aa._0 + a.aa._1 + b.aa._0 + b.aa._1;
+  } else if (a.tag == AA) {
+    return a.aa._0 + a.aa._1;
+  } else if (b.tag == BB) {
+    return b.aa._0 + b.aa._1;
+  } else {
+    return 0;
+  }
+}
+
+uint64_t t_add(T a, T b) {
+  if (a.tag == A && b.tag == A) {
+    return a.a._0 + b.a._0;
+  } else if (a.tag == AA) {
+    return a.a._0;
+  } else if (b.tag == BB) {
+    return b.a._0;
+  } else {
+    return 0;
+  }
+}
+
+TT tt_new(uint64_t a, uint64_t b) {
+  TT tt = {
+    .tag = AA,
+    .aa = {
+      ._0 = a,
+      ._1 = b,
+    },
+  };
+  return tt;
+}
+
+T t_new(uint64_t a) {
+  T t = {
+    .tag = A,
+    .a = {
+      ._0 = a,
+    },
+  };
+  return t;
+}

src/test/run-make-fulldeps/return-non-c-like-enum-from-c/Makefile

@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all:
+	$(CC) -c test.c -o $(call STATICLIB,test) $(EXTRACFLAGS) $(EXTRACXXFLAGS)
+	$(RUSTC) nonclike.rs -L$(TMPDIR) -ltest
+	$(call RUN,nonclike)

src/test/run-make-fulldeps/return-non-c-like-enum-from-c/nonclike.rs

@@ -0,0 +1,34 @@
+#![crate_type = "bin"]
+#![crate_name = "nonclike"]
+
+#[repr(C, u8)]
+pub enum TT {
+    AA(u64, u64),
+    BB,
+}
+
+#[repr(C,u8)]
+pub enum T {
+    A(u64),
+    B,
+}
+
+extern "C" {
+    pub fn t_new(a: u64) -> T;
+    pub fn tt_new(a: u64, b: u64) -> TT;
+}
+
+fn main() {
+    if let TT::AA(a, b) = unsafe { tt_new(10, 11) } {
+        assert_eq!(10, a);
+        assert_eq!(11, b);
+    } else {
+        panic!("expected TT::AA");
+    }
+
+    if let T::A(a) = unsafe { t_new(10) } {
+        assert_eq!(10, a);
+    } else {
+        panic!("expected T::A");
+    }
+}

src/test/run-make-fulldeps/return-non-c-like-enum-from-c/test.c

@@ -0,0 +1,61 @@
+#include <stdint.h>
+
+/* This is the code generated by cbindgen 0.12.1 for the `enum TT`
+ * type in nonclike.rs . */
+enum TT_Tag {
+  AA,
+  BB,
+};
+typedef uint8_t TT_Tag;
+
+typedef struct {
+  uint64_t _0;
+  uint64_t _1;
+} AA_Body;
+
+typedef struct {
+  TT_Tag tag;
+  union {
+    AA_Body aa;
+  };
+} TT;
+
+/* This is the code generated by cbindgen 0.12.1 for the `enum T` type
+ * in nonclike.rs . */
+enum T_Tag {
+  A,
+  B,
+};
+typedef uint8_t T_Tag;
+
+typedef struct {
+  uint64_t _0;
+} A_Body;
+
+typedef struct {
+  T_Tag tag;
+  union {
+    A_Body a;
+  };
+} T;
+
+TT tt_new(uint64_t a, uint64_t b) {
+  TT tt = {
+    .tag = AA,
+    .aa = {
+      ._0 = a,
+      ._1 = b,
+    },
+  };
+  return tt;
+}
+
+T t_new(uint64_t a) {
+  T t = {
+    .tag = A,
+    .a = {
+      ._0 = a,
+    },
+  };
+  return t;
+}