gnu: bcftools: Fix building on aarch64.

* gnu/packages/patches/bcftools-regidx-unsigned-char.patch: New file.
* gnu/packages/bioinformatics.scm (bcftools)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Register it.

gnu/local.mk

@@ -527,6 +527,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/awesome-reproducible-png.patch		\
   %D%/packages/patches/azr3.patch				\
   %D%/packages/patches/bash-completion-directories.patch	\
+  %D%/packages/patches/bcftools-regidx-unsigned-char.patch	\
   %D%/packages/patches/binutils-ld-new-dtags.patch		\
   %D%/packages/patches/binutils-loongson-workaround.patch	\
   %D%/packages/patches/binutils-mips-bash-bug.patch		\

gnu/packages/bioinformatics.scm

@@ -311,6 +311,7 @@ BAM files.")
               (sha256
                (base32
                 "0093hkkvxmbwfaa7905s6185jymynvg42kq6sxv7fili11l5mxwz"))
+              (patches (search-patches "bcftools-regidx-unsigned-char.patch"))
               (modules '((guix build utils)))
               (snippet
                ;; Delete bundled htslib.

gnu/packages/patches/bcftools-regidx-unsigned-char.patch

@@ -0,0 +1,16 @@
+Description: Fix test-regidx argument parsing on archs with unsigned char
+ On architectures where char is unsigned "c >= 0" was always true.
+Author: Adrian Bunk <bunk@debian.org>
+Bug-Debian: https://bugs.debian.org/865060
+
+--- a/test/test-regidx.c
++++ b/test/test-regidx.c
+@@ -336,7 +336,7 @@
+         {"seed",1,0,'s'},
+         {0,0,0,0}
+     };
+-    char c;
++    int c;
+     int seed = (int)time(NULL);
+     while ((c = getopt_long(argc, argv, "hvs:",loptions,NULL)) >= 0) 
+     {