gnu: findutils: Fix build with glibc 2.28.

* gnu/packages/patches/findutils-gnulib-libio.patch,
gnu/packages/patches/findutils-makedev.patch: New files.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/base.scm (findutils)[source](patches): Use them.

gnu/packages/patches/findutils-makedev.patch

@@ -0,0 +1,22 @@
+Include <sys/sysmacros.h> for "makedev".
+
+Taken from this gnulib commit:
+https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=4da63c5881f60f71999a943612da9112232b9161
+
+diff --git a/gl/lib/mountlist.c b/gl/lib/mountlist.c
+index bb4e4ee21..cf4020e2a 100644
+--- a/gl/lib/mountlist.c
++++ b/gl/lib/mountlist.c
+@@ -37,6 +37,12 @@
+ # include <sys/param.h>
+ #endif
+ 
++#if MAJOR_IN_MKDEV
++# include <sys/mkdev.h>
++#elif MAJOR_IN_SYSMACROS
++# include <sys/sysmacros.h>
++#endif
++
+ #if defined MOUNTED_GETFSSTAT   /* OSF_1 and Darwin1.3.x */
+ # if HAVE_SYS_UCRED_H
+ #  include <grp.h> /* needed on OSF V4.0 for definition of NGROUPS,