gnu: arb: Build with flint 2.6.

Backport an upstream patch to fix a compatibility issue with flint 2.6.

* gnu/packages/algebra.scm (arb): Add patch.
* gnu/packages/patches/arb-flint-2.6.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register new file.

gnu/local.mk

@@ -772,6 +772,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/antlr3-3_1-fix-java8-compilation.patch	\
   %D%/packages/patches/antlr3-3_3-fix-java8-compilation.patch	\
   %D%/packages/patches/apr-skip-getservbyname-test.patch	\
+  %D%/packages/patches/arb-flint-2.6.patch			\
   %D%/packages/patches/aspell-default-dict-dir.patch		\
   %D%/packages/patches/ath9k-htc-firmware-binutils.patch	\
   %D%/packages/patches/ath9k-htc-firmware-gcc.patch		\

gnu/packages/algebra.scm

@@ -504,7 +504,8 @@ fast arithmetic.")
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "05lpy3hkl5f8ik19aw40cqydrb932xaf2n8hbq9ib5dnk7f010p1"))))
+                "05lpy3hkl5f8ik19aw40cqydrb932xaf2n8hbq9ib5dnk7f010p1"))
+              (patches (search-patches "arb-flint-2.6.patch"))))
     (build-system gnu-build-system)
     (propagated-inputs
      `(("flint" ,flint)))               ; flint.h is included by arf.h

gnu/packages/patches/arb-flint-2.6.patch

@@ -0,0 +1,48 @@
+From d3d9983231e0f034e86a1e75761627eb8213b704 Mon Sep 17 00:00:00 2001
+From: fredrik <fredrik.johansson@gmail.com>
+Date: Wed, 29 Apr 2020 13:41:36 +0200
+Subject: [PATCH] handle flint incompatibilities
+
+---
+ fmpr.h        | 4 ++++
+ fmpz_extras.h | 4 ++++
+ 2 files changed, 8 insertions(+)
+
+diff --git a/fmpr.h b/fmpr.h
+index 2204d72e..c6a8c342 100644
+--- a/fmpr.h
++++ b/fmpr.h
+@@ -22,7 +22,11 @@
+ #include "flint/flint.h"
+ #include "flint/fmpz.h"
+ #include "flint/fmpq.h"
++#if __FLINT_RELEASE < 20600
+ #include "flint/config.h"
++#else
++#include "flint/flint-config.h"
++#endif
+ #include "fmpz_extras.h"
+ 
+ #ifndef flint_abort
+diff --git a/fmpz_extras.h b/fmpz_extras.h
+index 4fd0538f..486e28c8 100644
+--- a/fmpz_extras.h
++++ b/fmpz_extras.h
+@@ -43,6 +43,8 @@ fmpz_add_inline(fmpz_t z, const fmpz_t x, const fmpz_t y)
+         fmpz_add(z, x, y);
+ }
+ 
++#if __FLINT_RELEASE < 20600
++
+ static __inline__ void
+ fmpz_add_si(fmpz_t z, const fmpz_t x, slong y)
+ {
+@@ -61,6 +63,8 @@ fmpz_sub_si(fmpz_t z, const fmpz_t x, slong y)
+         fmpz_add_ui(z, x, -y);
+ }
+ 
++#endif
++
+ static __inline__ void
+ fmpz_add_si_inline(fmpz_t z, const fmpz_t x, slong y)
+ {