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