Use depends protoc for Linux wallet builds

contrib/build-linux-wallet.sh

@@ -6,6 +6,9 @@ JOBS="${JOBS:-1}"
 HOST="${HOST:-x86_64-pc-linux-gnu}"
 PREFIX="$ROOT/depends/$HOST"
 BASE_CONFIG="$PREFIX/share/config.site"
+BUILD_HOST="${BUILD_HOST:-$("$ROOT/depends/config.guess")}"
+NATIVE_BIN="$ROOT/depends/build/$BUILD_HOST/bin"
+PROTOC="$NATIVE_BIN/protoc"
 
 require_cmd() {
   if ! command -v "$1" >/dev/null 2>&1; then
@@ -33,6 +36,7 @@ require_cmd ninja
 echo "Building native depends for $HOST..."
 make -C depends HOST="$HOST" NO_QT=0 -j"$JOBS"
 require_path "$BASE_CONFIG"
+require_path "$PROTOC"
 
 if [[ ! -f configure ]]; then
   ./autogen.sh
@@ -44,7 +48,8 @@ CONFIG_SITE="$BASE_CONFIG" ./configure \
   --disable-tests \
   --disable-bench \
   --with-gui=qt6 \
-  --with-qtdbus=no
+  --with-qtdbus=no \
+  --with-protoc-bindir="$NATIVE_BIN"
 
 echo "Building Ubuntu Qt wallet with JOBS=$JOBS..."
 make -j"$JOBS"

doc/build-menu.md

@@ -44,7 +44,8 @@ instead of being required as Ubuntu system development packages.
 
 The Linux Qt wallet option also installs Ubuntu desktop development headers
 needed by Qt's xcb platform plugin, including fontconfig, freetype, xcb, and
-xkbcommon packages.
+xkbcommon packages. The wallet helper uses the matching `protoc` built by
+`depends/`, so a system protobuf compiler is not required.
 
 Defaults
 --------