add CPU Frequency/overclock setting to libretro core

[QcSamuel]

[jfroco]

That windows is for editing the machine's config.ini file. You can do the same on RetroArch by changing that parameter directly in your system/Machines folder.

Example:

system/Machines/SEGA - SG-1000/config.ini:

[CMOS]
Enable CMOS=0
Battery Backed=0
[Video]
version=TMS99x8A
vram size=16kB
[Subslotted Slots]
slot 0=0
slot 1=0
slot 2=0
slot 3=0
[External Slots]
slot A=1 0
slot B=1 0
[FDC]
Count=2
[CPU]
Z80 Frequency=3579545Hz
[Board]
type=SG-1000
[Slots]
0 0 6 2 111 "" ""

Hope this helps.