Issue errors if array dimensions are negative or too large to fit in 32 bits.

tests_errors/array-dim-huge.ispc

@@ -0,0 +1,7 @@
+// Array dimension must be representable with a 32-bit integer.
+
+struct foo {
+    int x[0xffffffffffff];
+};
+
+

tests_errors/array-dim-negative.ispc

@@ -0,0 +1,7 @@
+// Array dimension must be non-negative
+
+struct foo {
+    int x[-1];
+};
+
+