Build libnettle with assembly code (#1292)

* Build libnettle with assembler code

* Add .gitattributes for shell script

* Patch nettle for CPU feature detection on Android

* Don't build libnettle at configuration time

* Fix build

* Refine

app/src/main/cpp/configure_nettle.sh

@@ -0,0 +1,6 @@
+TOOLCHAIN=$ANDROID_HOME/ndk/$1/toolchains/llvm/prebuilt/$(uname -s | tr '[:upper:]' '[:lower:]')-x86_64/bin
+TARGET=$2
+./configure --host=$TARGET --disable-public-key --disable-dependency-tracking \
+  AR=$TOOLCHAIN/llvm-ar \
+  CC="$TOOLCHAIN/clang -target $TARGET" \
+  RANLIB=$TOOLCHAIN/llvm-ranlib