mpir: fix build failure on MIPS

Fixes:

  http://autobuild.buildroot.net/results/3de0ef545a7303ec6564ecf1a1da3dd539957ed4/

Signed-off-by: Semyon Kolganov <semenak94@mail.ru>
[Thomas: remove bogus PowerPC stuff, fix n64 specification, rework
commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/mpir/mpir.mk

@@ -12,4 +12,12 @@ MPIR_LICENSE_FILES = COPYING.LIB
 MPIR_INSTALL_STAGING = YES
 MPIR_DEPENDENCIES = gmp host-yasm
 
+ifeq ($(BR2_MIPS_NABI32),y)
+MPIR_CONF_OPTS += ABI=n32
+endif
+
+ifeq ($(BR2_MIPS_NABI64),y)
+MPIR_CONF_OPTS += ABI=64
+endif
+
 $(eval $(autotools-package))