compiler: c'str' now has type charptr

vlib/compiler/tests/cstrings_test.v

@@ -0,0 +1,9 @@
+
+fn C.puts(charptr) int
+
+fn test_cstring(){
+  h := c'world'
+  C.puts(c'hello')
+  C.puts(h)
+  assert true
+}