fix: darwin platform signal list

[BhautikChudasama]

Description

SIGCLD, SIGPOLL, SIGPWR, SIGSTKFLT, SIGUNUSED are not defined in the darwin platform. So removed mentioned signal for the darwin platform.

Fixes # (issue)

• Fixed signal not defined for darwin platform.

Type of change

• Separated darwin, and other platform signals files.

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have read the contribution guidelines and followed it as far as possible.
• I have performed a self-review of my own code (if applicable)
• I have commented my code, particularly in hard-to-understand areas (if applicable)
• I have run go fmt on my code (reference)
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• Any dependent and pending changes have been merged and published