Hello He,
I'm not aware of such document.
EWL comes from Freescale/NXP, NewLib is a standard distributed under freeware license:
https://sourceware.org/newlib/
Some introduction can be found S32DS user guide (c:\NXP\S32DS_ARM_v2.2\S32DS\help\pdf\S32DS_ARM_User_Guide.pdf):

Documentation for EWL can be found here:
c:\NXP\S32DS_ARM_v2.2\S32DS\help\resources\manuals\ewl_c_reference.pdf
Regards,
Lukas