Add allocation unit tests.

tests/system/alloc.nim

@@ -0,0 +1,45 @@
+var x: ptr int
+
+x = cast[ptr int](alloc(7))
+assert x != nil
+
+x = alloc(int, 3)
+assert x != nil
+x.dealloc()
+
+x = alloc0(int, 4)
+assert cast[ptr array[4, int]](x)[0] == 0
+assert cast[ptr array[4, int]](x)[1] == 0
+assert cast[ptr array[4, int]](x)[2] == 0
+assert cast[ptr array[4, int]](x)[3] == 0
+
+x = cast[ptr int](x.realloc(2))
+assert x != nil
+
+x = x.reallocType(4)
+assert x != nil
+x.dealloc()
+
+x = cast[ptr int](allocShared(100))
+assert x != nil
+deallocShared(x)
+
+x = allocShared(int, 3)
+assert x != nil
+x.deallocShared()
+
+x = allocShared0(int, 3)
+assert x != nil
+assert cast[ptr array[3, int]](x)[0] == 0
+assert cast[ptr array[3, int]](x)[1] == 0
+assert cast[ptr array[3, int]](x)[2] == 0
+
+x = cast[ptr int](reallocShared(x, 2))
+assert x != nil
+
+x = reallocType(x, 12)
+assert x != nil
+
+x = reallocSharedType(x, 1)
+assert x != nil
+x.deallocShared()