Hello again. I have taken note of the performance delays when you are building a project that has a large (30k) compile command. We will replicate and see what is causing the delays in RTist. Thanks again for providing the issue to us.
With a little investigation I found a work around that may point to the root cause. All of the discussion below references the generated project "C/C++ Build" properties accessed by right clicking on the generated project, selecting "Properties", then selecting "C/C++ Build". By default on the "Tool Chain Editor" dialog, the "Current builder" is set to "com.ibm.xtools.umldt.rt.cpp.makefile.builder" which exhibits the slow compiles when the compile command is long as described above. A work around is to uncheck "Display compatible toolchains only" and set the "Current toolchain" to "No ToolChain". (The toolchain specified in libset.mk will be used if a complete path is provided in the "CC =" and "AR_CMD = " variables.) Once this is done, on the C/C++ Build/Behavior tab set "Enable parallel build" with "Use optimal jobs". These two changes will result in fast compiles like at the command-line or when the compile line is fairly short.
Before building after making the above changes, be sure and "Clean Project".