checkinstall: fix build with glibc-2.19

pkgs/tools/package-management/checkinstall/default.nix

···
 
     # Fix a `conflicting types for 'scandir'' error on Glibc 2.11.
     ./scandir.patch
+
+    # Fix a `conflicting types for 'readlink'' error since Glibc 2.19
+    ./readlink-types.patch
   ]
 
   ++ stdenv.lib.optional (stdenv.system == "x86_64-linux") 

pkgs/tools/package-management/checkinstall/readlink-types.patch

···
+Extracted from Arch's patch
+https://projects.archlinux.org/svntogit/community.git/tree/trunk/build-fix.patch?h=packages/checkinstall
+diff -wbBur checkinstall-1.6.2/installwatch/installwatch.c checkinstall-1.6.2.my/installwatch/installwatch.c
+--- checkinstall-1.6.2/installwatch/installwatch.c	2008-11-16 19:20:53.000000000 +0300
++++ checkinstall-1.6.2.my/installwatch/installwatch.c	2010-01-15 18:55:50.112716628 +0300
+@@ -2938,13 +2938,8 @@
+ 	return result;
+ }
+ 
+-#if (GLIBC_MINOR <= 4)
+-int readlink(const char *path,char *buf,size_t bufsiz) {
+-	int result;
+-#else
+ ssize_t readlink(const char *path,char *buf,size_t bufsiz) {
+ 	ssize_t result;
+-#endif
+ 	instw_t instw;
+ 	int status;
+