add json11 package (#33)

* add libyuv package

* update libyuv to upstream 1922

* add json11 package

json11/build.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null && pwd)"
+cd "$DIR"
+
+VERSION="db00e9369a92aa74bf630a2ffb092a4b0b132c01"
+INSTALL_DIR="$DIR/json11/install"
+VERSION_FILE="$INSTALL_DIR/VERSION"
+
+# Idempotent: skip if already built at this source revision.
+if [ -f "$INSTALL_DIR/lib/libjson11.a" ] && [ -f "$INSTALL_DIR/include/json11/json11.hpp" ] && \
+  [ -f "$VERSION_FILE" ] && [ "$(cat "$VERSION_FILE")" = "$VERSION" ]; then
+  echo "json11 already present, skipping build."
+  exit 0
+fi
+
+if [ ! -d "$DIR/json11-src/.git" ]; then
+  git clone https://github.com/dropbox/json11.git json11-src
+fi
+
+git -C json11-src fetch --force origin
+git -C json11-src checkout --force "$VERSION"
+
+BUILD_DIR="$DIR/build"
+rm -rf "$BUILD_DIR" "$INSTALL_DIR"
+mkdir -p "$BUILD_DIR" "$INSTALL_DIR/lib" "$INSTALL_DIR/include/json11"
+
+CXX="${CXX:-c++}"
+AR="${AR:-ar}"
+
+"$CXX" -std=c++11 -fPIC -O2 -c "$DIR/json11-src/json11.cpp" -o "$BUILD_DIR/json11.o"
+"$AR" rcs "$INSTALL_DIR/lib/libjson11.a" "$BUILD_DIR/json11.o"
+cp "$DIR/json11-src/json11.hpp" "$INSTALL_DIR/include/json11/json11.hpp"
+echo "$VERSION" > "$VERSION_FILE"
+
+# Keep workspace small and deterministic across builds.
+rm -rf "$DIR/json11-src" "$BUILD_DIR"
+
+echo "Installed json11 to $INSTALL_DIR"
+du -sh "$INSTALL_DIR"