Fix build on powerpc64le (#5884)

Without compiling ppc-simd.cpp, linking fails with:
: && /usr/bin/c++ -O2 -pipe -fstack-protector-strong -isystem /usr/local/include -fno-strict-aliasing  -isystem /usr/local/include -O2 -pipe -fstack-protector-strong -isystem /usr/local/include -fno-strict-aliasing  -isystem /usr/local/include -Wl,--as-needed -fstack-protector-strong -L/usr/local/lib src/tests/CMakeFiles/tests.dir/common/bit_field.cpp.o src/tests/CMakeFiles/tests.dir/common/param_package.cpp.o src/tests/CMakeFiles/tests.dir/core/arm/arm_test_common.cpp.o src/tests/CMakeFiles/tests.dir/core/arm/dyncom/arm_dyncom_vfp_tests.cpp.o src/tests/CMakeFiles/tests.dir/core/core_timing.cpp.o src/tests/CMakeFiles/tests.dir/core/file_sys/path_parser.cpp.o src/tests/CMakeFiles/tests.dir/core/hle/kernel/hle_ipc.cpp.o src/tests/CMakeFiles/tests.dir/core/memory/memory.cpp.o src/tests/CMakeFiles/tests.dir/core/memory/vm_manager.cpp.o src/tests/CMakeFiles/tests.dir/audio_core/decoder_tests.cpp.o src/tests/CMakeFiles/tests.dir/tests.cpp.o -o bin/Release/tests  src/common/libcommon.a  src/core/libcore.a  src/video_core/libvideo_core.a  src/audio_core/libaudio_core.a  src/core/libcore.a  src/video_core/libvideo_core.a  src/audio_core/libaudio_core.a  externals/soundtouch/libSoundTouch.a  externals/teakra/src/libteakra.a  /usr/local/lib/libSDL2main.a  /usr/local/lib/libSDL2.so  externals/cubeb/libcubeb.a  -lpthread  externals/cryptopp/libcryptopp.a  src/web_service/libweb_service.a  src/network/libnetwork.a  externals/enet/libenet.a  externals/libressl/tls/libtls.a  externals/libressl/ssl/libssl.a  externals/libressl/crypto/libcrypto.a  externals/lurlparser/liblurlparser.a  /usr/local/lib/libavformat.so  /usr/local/lib/libavcodec.so  /usr/local/lib/libswscale.so  /usr/local/lib/libswresample.so  /usr/local/lib/libavutil.so  src/common/libcommon.a  externals/fmt/libfmt.a  externals/zstd/build/cmake/lib/libzstd.a
 -pthread  /usr/local/lib/libboost_serialization.a  externals/glad/libglad.a && :
ld: error: undefined symbol: CryptoPP::CPU_ProbeAltivec()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a

ld: error: undefined symbol: CryptoPP::CPU_ProbePower7()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a

ld: error: undefined symbol: CryptoPP::CPU_ProbePower8()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a

ld: error: undefined symbol: CryptoPP::CPU_ProbeAES()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a

ld: error: undefined symbol: CryptoPP::CPU_ProbeSHA256()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a

ld: error: undefined symbol: CryptoPP::CPU_ProbeSHA512()
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(CryptoPP::DetectPowerpcFeatures()) in archive externals/cryptopp/libcryptopp.a
>>> referenced by cpu.cpp
>>>               cpu.cpp.o:(_GLOBAL__I_000260) in archive externals/cryptopp/libcryptopp.a
c++: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.

externals/cryptopp/CMakeLists.txt

@@ -157,6 +157,7 @@ set(cryptopp_SOURCES
         cryptopp/neon-simd.cpp
         cryptopp/oaep.cpp
         cryptopp/osrng.cpp
+        cryptopp/ppc-simd.cpp
         cryptopp/pubkey.cpp
         cryptopp/queue.cpp
         cryptopp/randpool.cpp