botan: fix mips64 build using n32 ABI

Remove explicit -mabi parameter, and let the external toolchain wrapper set
the correct -mabi.

Fixes:
http://autobuild.buildroot.net/results/8fb/8fb8621bc5175f593de4ad0f005a5c7ffd4d9241/

Cc: Francois Perrad <fperrad@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/botan/0001-remove-mips64-explicit-mabi.patch

@@ -0,0 +1,18 @@
+Remove explicit mips64 -mabi parameter
+
+This breaks when building for n32 ABI on mips64.
+
+Signed-off-by: Baruch Siach <baruch@tkos.co.il>
+---
+
+diff -Nuar Botan-1.10.8-orig/src/build-data/cc/gcc.txt Botan-1.10.8/src/build-data/cc/gcc.txt
+--- Botan-1.10.8-orig/src/build-data/cc/gcc.txt	2014-04-10 17:11:44.000000000 +0300
++++ Botan-1.10.8/src/build-data/cc/gcc.txt	2014-10-23 09:20:34.506722323 +0300
+@@ -92,7 +92,6 @@
+ # The 'linking' bit means "use this for both compiling *and* linking"
+ <mach_abi_linking>
+ x86_64  -> "-m64"
+-mips64  -> "-mabi=64"
+ s390    -> "-m31"
+ s390x   -> "-m64"
+ sparc32 -> "-m32 -mno-app-regs"