package/cryptopp: disable neon if needed

Fix the following build failure raised since commit
bf4cf9de833e2d571d98d1ca935ea08a3468e463:

In file included from aria_simd.cpp:18:0:
/home/buildroot/autobuild/instance-3/output-1/host/opt/ext-toolchain/lib/gcc/arm-none-linux-gnueabi/4.8.3/include/arm_neon.h:32:2: error: #error You must enable NEON instructions (e.g. -mfloat-abi=softfp -mfpu=neon) to use arm_neon.h
 #error You must enable NEON instructions (e.g. -mfloat-abi=softfp -mfpu=neon) to use arm_neon.h
  ^

Fixes:
 - http://autobuild.buildroot.org/results/e4fd947c118174a4fad62cbed18816f02d39ec25

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/cryptopp/cryptopp.mk

@@ -47,6 +47,10 @@ ifneq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_9),y)
 CRYPTOPP_CXXFLAGS += -DCRYPTOPP_DISABLE_AVX2
 endif
 
+ifneq ($(BR2_ARM_CPU_HAS_NEON),y)
+CRYPTOPP_CXXFLAGS += -DCRYPTOPP_DISABLE_ARM_NEON
+endif
+
 CRYPTOPP_MAKE_OPTS = \
 	$(TARGET_CONFIGURE_OPTS) \
 	CXXFLAGS="$(CRYPTOPP_CXXFLAGS)"