libtommath: build with -fPIC

This fixes the build on x86_64, see:

  http://autobuild.buildroot.net/results/212/212469db5dc8399070390603c0fdf7f12b130cda/

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libtommath/libtommath.mk

@@ -13,7 +13,7 @@ LIBTOMMATH_INSTALL_STAGING = YES
 LIBTOMMATH_INSTALL_TARGET = NO  # only static library
 
 define LIBTOMMATH_BUILD_CMDS
-	$(MAKE) -C $(@D) $(TARGET_CONFIGURE_OPTS) CFLAGS="-I./ $(TARGET_CFLAGS)"
+	$(MAKE) -C $(@D) $(TARGET_CONFIGURE_OPTS) CFLAGS="-I./ -fPIC $(TARGET_CFLAGS)"
 endef
 
 define LIBTOMMATH_INSTALL_STAGING_CMDS