pkgutils: add mtune optimization for rpi3 CFLAGS

[sepen]

Currently in the pkgutils port, we have the following CFLAGS in pkgmk.conf for the rpi3

export CFLAGS="-O2 -pipe -march=armv8-a+crc -mabi=lp64 -mlittle-endian"

I think -mlittle-endian can be omitted in the flags:

• on ARMv7 or earlier, specifying endianness might be more relevant, as some older ARM implementations could be big-endian but for ARMv8, little-endian is the standard
• you would only need to specify it if you’re working with specific hardware that uses a non-standard endianness, like big-endian, which is rare for ARMv8 (this is not the case for rpi3)

On the other hand I would add -mtune=cortex-a53 since it could provide some optimizations so we can maximize performance. From the GCC docs: -mtune helps the compiler generate more efficient code by optimizing for the characteristics of that particular architecture.

I can't verify this on a rpi3b+ but at least on my rpi3b (v1.2) I haven't had any problems using these flags.

Comments? (cc @pitill0)

---

Flags that I'm using

export CFLAGS="-O2 -pipe -march=armv8-a+crc -mabi=lp64 -mtune=cortex-a53"

Output for arminfo.sh

HOSTNAME   rpi3b
MODEL      unknown
FEATURES   fp asimd evtstrm crc32
MACHTYPE   aarch64-unknown-linux-gnu
CFLAGS     -march=armv8-a+crc -mabi=lp64 -mtune=cortex-a53
MAKEFLAGS  -j4

Output for lscpu on rpi3b

Architecture:            aarch64
  CPU op-mode(s):        32-bit, 64-bit
  Byte Order:            Little Endian
CPU(s):                  4
  On-line CPU(s) list:   0-3
Vendor ID:               ARM
  Model name:            Cortex-A53
    Model:               4
    Thread(s) per core:  1
    Core(s) per cluster: 4
    Socket(s):           -
    Cluster(s):          1
    Stepping:            r0p4
    CPU(s) scaling MHz:  50%
    CPU max MHz:         1200.0000
    CPU min MHz:         600.0000
    BogoMIPS:            38.40
    Flags:               fp asimd evtstrm crc32