fix: disable GDB in toolchain to resolve build failures

The firmware builds were failing during toolchain compilation due to
GDB (GNU debugger) missing testsuite/Makefile. This is a known issue
with OpenWrt's GDB toolchain component.

Error:
  Missing testsuite/Makefile
  make[7]: *** [Makefile:1992: subdir_do] Error 1
  ERROR: toolchain/gdb failed to build

Solution:
- Disable GDB in toolchain with '# CONFIG_GDB is not set'
- GDB is not needed for building firmware images
- Only useful for on-device debugging (can be installed separately)
- Enable BUILD_LOG for better debugging

This fix applies to both:
- Local firmware builds (local-build.sh)
- GitHub Actions firmware builds (build-secubox-images.yml)

Impact:
- Toolchain will compile successfully
- Firmware images will be generated
- Build time remains the same (1-2 hours for full build)
- No impact on firmware functionality

Tested with:
- OpenWrt 23.05.5
- Target: mvebu/cortexa72 (MOCHAbin)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.github/workflows/build-secubox-images.yml

@@ -236,7 +236,11 @@ jobs:
           CONFIG_TARGET_ROOTFS_EXT4FS=y
           CONFIG_TARGET_KERNEL_PARTSIZE=32
           CONFIG_TARGET_ROOTFS_PARTSIZE=512
-          
+
+          # Disable GDB in toolchain (fixes build issues)
+          # CONFIG_GDB is not set
+          CONFIG_BUILD_LOG=y
+
           # Base packages
           CONFIG_PACKAGE_luci=y
           CONFIG_PACKAGE_luci-ssl=y

secubox-tools/local-build.sh

@@ -937,6 +937,10 @@ CONFIG_TARGET_ROOTFS_EXT4FS=y
 CONFIG_TARGET_KERNEL_PARTSIZE=32
 CONFIG_TARGET_ROOTFS_PARTSIZE=512
 
+# Disable GDB in toolchain (fixes build issues)
+# CONFIG_GDB is not set
+CONFIG_BUILD_LOG=y
+
 # Base packages
 CONFIG_PACKAGE_luci=y
 CONFIG_PACKAGE_luci-ssl=y