mdadm: fix *-musl build

srcpkgs/mdadm/patches/sysmacros_h.patch

@@ -0,0 +1,13 @@
+--- mdadm.h	2018-10-01 20:26:06.000000000 +0200
++++ mdadm.h	2019-12-27 07:24:26.224920452 +0100
+@@ -45,10 +45,7 @@
+ #include	<errno.h>
+ #include	<string.h>
+ #include	<syslog.h>
+-#ifdef __GLIBC__
+-/* Newer glibc requires sys/sysmacros.h directly for makedev() */
+ #include	<sys/sysmacros.h>
+-#endif
+ #ifdef __dietlibc__
+ #include	<strings.h>
+ /* dietlibc has deprecated random and srandom!! */