[DOC] Adding item to FAQ for 2025.2

[lapel22]

Added new FAQ item per Jira [DOC-13288] (https://jira.devtools.intel.com/browse/DOC-13288). Please review, approve, and merge if it looks okay.

[zhiweij1]

-ignore-unknown is not a dpct's option nor a clang's option.

[zhiweij1]

(base) zhiwei@zhiwei-ubuntu:~/testfolder$ rm -rf out && dpct --out-root out -p . --extra-arg="-ignore-unknown"
error: dpct/c2s ignoring argument: '-gencode=arch=compute_50,code="sm_50,compute_50"'
error: dpct/c2s ignoring argument: '-ignore-unknown'
warning: CUDA version 12.8 is only partially supported [-Wunknown-cuda-version]
Parsing: /home/zhiwei/testfolder/test.cu
Analyzing: /home/zhiwei/testfolder/test.cu
Migrating: /home/zhiwei/testfolder/test.cu
Processed 1 file(s) in -in-root folder "/home/zhiwei/testfolder"

See Diagnostics Reference to resolve warnings and complete the migration:
https://oneapi-src.github.io/SYCLomatic/dev_guide/reference/diagnostics-reference.html

(base) zhiwei@zhiwei-ubuntu:~/testfolder$ rm -rf out && dpct --out-root out -p . -ignore-unknown
Unknown command line argument '-ignore-unknown'.  Try: 'dpct --help'
Did you mean '--report-only'?
dpct exited with code: -16 (Option parsing error, run 'dpct --help' to see supported options and values.)

(base) zhiwei@zhiwei-ubuntu:~/testfolder$