Added testcase for Issue #1408.

test/val/bug1408.c

@@ -0,0 +1,41 @@
+/* Bug #1408: Signed char type comparisons with unsigned numeric constants */
+
+#include <stdio.h>
+
+static int failures = 0;
+static signed char x = -1;
+
+int main(void)
+{
+    if (!(x > -2u)) {
+        printf("x > -2u should be true\n");
+        ++failures;
+    }
+    if (!(x > 0u)) {
+        printf("x > 0u should be true\n");
+        ++failures;
+    }
+    if (!(x > 255u)) {
+        printf("x > 255u should be true\n");
+        ++failures;
+    }
+
+    if (!(-2u < x)) {
+        printf("-2u < x should be true\n");
+        ++failures;
+    }
+    if (!(0u < x)) {
+        printf("0u < x should be true\n");
+        ++failures;
+    }
+    if (!(255u < x)) {
+        printf("255u < x should be true\n");
+        ++failures;
+    }
+
+    if (failures != 0) {
+        printf("Failures: %d\n", failures);
+    }
+
+    return failures;
+}