This contains the lpc code for the c15. It can be built using cmake and any arm toolchain. Therefore you'll find a toolchainfile in the cmake folder. For debugging, openocd is used. Any JTGA Adapter compatible to openocd could possibly be used for debugging. You might have to change the configuration file in openocd/nonlinear-lpc.cfg.
OpenOCD set's up as GDB server. So you can use any GDB client, to debug. Even over network, if necessary. This process is very well documented
mkdir -p build && cd build
cmake ../ -DCMAKE_TOOLCHAIN_FILE=../cmake/arm-gcc-toolchain.cmake -DCMAKE_BUILD_TYPE=Debug
make
You can use OpenOCD to program your flash. Either by using OpenOCD as a GDB Server or by using OpenOCD's own Flash Programming Commands
openocd -f openocd/nonlinear-lpc.cfg
Since this setup very similar to many open source IDE's way of doing things such as [eclipse with cdt plugin][https://www.eclipse.org/cdt/] or [qtcreator with baremetal plugin][https://doc.qt.io/qtcreator/creator-developing-baremetal.html] it should be fairly easy to setup an IDE.