fixes #13698 [backport:1.2] (#14175)

lib/system/memory.nim

@@ -45,9 +45,9 @@ proc nimCmpMem*(a, b: pointer, size: Natural): cint {.compilerproc, nonReloadabl
       if d != 0: return d
       inc i
 
-proc nimCStrLen*(a: cstring): csize_t {.compilerproc, nonReloadable, inline.} =
+proc nimCStrLen*(a: cstring): int {.compilerproc, nonReloadable, inline.} =
   when useLibC:
-    c_strlen(a)
+    cast[int](c_strlen(a))
   else:
     var a = cast[ptr byte](a)
     while a[] != 0:

tests/misc/trangechecks.nim

@@ -41,3 +41,8 @@ except OverflowDefect, RangeDefect:
   echo x
 
 echo expected == 4
+
+# bug #13698
+var
+  x45 = "hello".cstring
+  p = x45.len.int32