in tools/lib/gcc/arm-none-eabi/4.8.4/include/stdarg.h, but apparently the file tools/redlib/include/stdarg.h, which omits this definition, i.e. only defines
Content originally posted in LPCWare by lpcxpresso-support on Wed Feb 04 01:40:06 MST 2015 Redlib does not implement a full C99 library, only part of it. If you want full C99 library support, you need to reconfigure your project to use Newlib / NewlibNano. If you reconfigure correctly, then the appropriate C library header files will then get picked up by the compiler.