graphics/jpeg-turbo: Update to 2.1.5.1

• Minor rearrangement of Makefile for better readbility
• Adjust port to not override cflags defined by framework

Changelog:
https://github.com/libjpeg-turbo/libjpeg-turbo/releases/tag/2.1.5.1

PR: 269449
Reviewed by: desktop (tcberner)
Exp-run by: antoine