2.3.2. The RVCT31INC environment variable
The RVCT31INC environment variable points to the location of the included header and source files provided with RVCT. Do not change this environment variable. If you want to include files from other locations, use the ‑I and ‑J command‑line options as required.
When compiling, directories specified with RVCT31INC are searched immediately after directories specified by the ‑I option have been searched. If you use the ‑J option, RVCT31INC is ignored.