If you still see this post and you have more expert views on this topic please share, but I found a way to add NXP GCC to S32DS.
***Adding NXP GCC to S32DS
If you go to Window->Prefrences->S32DS Design Stduio for S32 Platform->S32DS Variables->GCC Toolchain
you can see some expected directories for different GCC versions and types. I just found the correct directory C:\NXP\S32DS.3.6.4\S32DS\build_tools\gcc_v9.2\gcc-9.2-arm32-eabi and pasted the toolchain files there.
*** Getting NXP GCC
To get the NXP GCC 9.2 or any other version you can search "S32 Compilers for S32 Design Studio" and you are provided with different versions, get it from there.
*** To Add RTD SDK to S32DS
Download and install the .exe and then there is also a updatesite zip file like SW32K1_RTD_4.4_1.0.1_HF01_DS_updatesite_D2209.zip after installing go to Help->Install new software->Add->Archive and select the upsatesite zip file.
*** To add a IAR, DIAB, GHS toolchains
I found the documentation from RTD files. There is howto file in
C:\NXP\SW32K1_S32M24x_RTD_4.4_3.0.0_QLP02\eclipse\plugins\BaseNXP_TS_T40D2M30I0R0\doc\howto
It points to HOWTO: Install IAR Eclipse plug-in into S32 Design Studio for ARM
and HOWTO: Install Wind River compiler Eclipse plug-in into S32 Design Studio
and HOWTO: Install GHS Compiler Plugin