build: install cross-compiler deps for keeper CI builds

Update the GitHub Actions workflow to install cmake and mipsel
cross-compiler before building keeper targets.

Update evmone-build.sh to detect available mipsel cross-compilers:
prefer mipsel-linux-gnu-gcc (Debian/Ubuntu), fall back to
mips64-linux-gnu-gcc with -EL -mabi=32 flags (Fedora).

.github/workflows/go.yml

@@ -49,6 +49,12 @@ jobs:
           go-version: '1.25'
           cache: false
 
+      - name: Install build dependencies
+        run: |
+          apt-get update
+          apt-get -yq --no-install-suggests --no-install-recommends install \
+            cmake g++ gcc-mipsel-linux-gnu g++-mipsel-linux-gnu
+
       - name: Build
         run: go run build/ci.go keeper
 

build/evmone-build.sh

@@ -7,6 +7,28 @@ TARGET="${1:-native}"
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 EVMONE_DIR="$SCRIPT_DIR/../evmone"
 
+# Detect mipsel cross-compiler: prefer mipsel-linux-gnu-gcc,
+# fall back to mips64-linux-gnu-gcc with -EL -mabi=32 flags.
+find_mipsel_cc() {
+    if command -v mipsel-linux-gnu-gcc &>/dev/null; then
+        echo "mipsel-linux-gnu-gcc"
+    elif command -v mips64-linux-gnu-gcc &>/dev/null; then
+        echo "mips64-linux-gnu-gcc"
+    else
+        return 1
+    fi
+}
+
+find_mipsel_cxx() {
+    if command -v mipsel-linux-gnu-g++ &>/dev/null; then
+        echo "mipsel-linux-gnu-g++"
+    elif command -v mips64-linux-gnu-g++ &>/dev/null; then
+        echo "mips64-linux-gnu-g++"
+    else
+        return 1
+    fi
+}
+
 # Map Go arch names to build directories and CMake settings
 case "$TARGET" in
     native|amd64)
@@ -22,12 +44,19 @@ case "$TARGET" in
         CMAKE_EXTRA="-DCMAKE_SYSTEM_PROCESSOR=aarch64 -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc -DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++"
         ;;
     mipsle)
-        if ! command -v mipsel-linux-gnu-gcc &>/dev/null; then
-            echo "Skipping mipsle build: cross-compiler not found"
-            exit 0
-        fi
+        MIPSEL_CC=$(find_mipsel_cc) || { echo "Skipping mipsle build: cross-compiler not found"; exit 0; }
+        MIPSEL_CXX=$(find_mipsel_cxx) || { echo "Skipping mipsle build: cross-compiler not found"; exit 0; }
         BUILD_DIR="$EVMONE_DIR/build-mipsle"
-        CMAKE_EXTRA="-DCMAKE_SYSTEM_PROCESSOR=mipsel -DCMAKE_C_COMPILER=mipsel-linux-gnu-gcc -DCMAKE_CXX_COMPILER=mipsel-linux-gnu-g++ -DCMAKE_SYSTEM_NAME=Linux"
+        MIPS_FLAGS=""
+        # mips64 compiler needs explicit flags for little-endian 32-bit
+        if [[ "$MIPSEL_CC" == *mips64* ]]; then
+            MIPS_FLAGS="-EL -mabi=32"
+        fi
+        CMAKE_EXTRA="-DCMAKE_SYSTEM_NAME=Linux -DCMAKE_SYSTEM_PROCESSOR=mipsel"
+        CMAKE_EXTRA="$CMAKE_EXTRA -DCMAKE_C_COMPILER=$MIPSEL_CC -DCMAKE_CXX_COMPILER=$MIPSEL_CXX"
+        if [ -n "$MIPS_FLAGS" ]; then
+            CMAKE_EXTRA="$CMAKE_EXTRA -DCMAKE_C_FLAGS=$MIPS_FLAGS -DCMAKE_CXX_FLAGS=$MIPS_FLAGS"
+        fi
         ;;
     *)
         echo "Unknown target: $TARGET" >&2