cocci: do not directly access the .d_type member in struct dirent

Add a rule to catch direct access to the .d_type member and use
DTYPE() macro instead, except in the emulation code paths that work
on platforms that do have the member.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

contrib/coccinelle/dtype.cocci

@@ -0,0 +1,8 @@
+@@
+identifier f != { finddata2dirent, precompose_utf8_readdir };
+struct dirent *E;
+@@
+  f(...) {<...
+- E->d_type
++ DTYPE(E)
+  ...>}