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.

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

Checklist:

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

[gedw99]

This works for me on m2 Mac.

However there is a warning of

iostat_darwin.c:28:2: warning: 'IOMasterPort' is deprecated: first deprecated in macOS 12.0 [-Wdeprecated-declarations]
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/IOKit.framework/Headers/IOKitLib.h:143:1: note: 'IOMasterPort' has been explicitly marked deprecated here
# github.com/shirou/gopsutil/host
smc_darwin.c:75:41: warning: 'kIOMasterPortDefault' is deprecated: first deprecated in macOS 12.0 [-Wdeprecated-declarations]
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/IOKit.framework/Headers/IOKitLib.h:133:19: note: 'kIOMasterPortDefault' has been explicitly marked deprecated here