time_unix: namespace zephyr headers

[uLipe]

After version 3, the Zephyr RTOS requires to namespace all its headers with zephyr before including any other header file that belongs to it, this PR checks the version o major number of the kernel and when above 3, namespace the Zephyr specific posix timer implementation.

[uLipe]

CC: @pablogs9

[uLipe]

@clalancette @ahcorde PTAL

[uLipe]

@pablogs9 @clalancette @ahcorde PTAL again.

[uLipe]

@fujitatomoya PTAL again also.

[pablogs9]

The new way to check version LGTM

[clalancette]

This is pretty messy, but if this makes it work, it is OK (actually this whole file is messy, but that's a separate problem).

Will run CI on it next.

[clalancette]

CI:

• Linux
• Linux-aarch64
• Windows

[uLipe]

@clalancette , I agree on you, the solution is not the most elegant but needed to make this supported across Zephyr versions 2.7 and 3.1

the header namespacing in Zephyr is introducing the same problem in others external modules .

[fujitatomoya]

good to go with green CI.

[clalancette]

Basically by definition, this change can't have made the one test on Windows fail. That one is flaky every once in a while anyway. Going ahead and merging this.

[pablogs9]

PTAL here: micro-ROS/micro_ros_zephyr_module#85 (comment)
Zephyr 2.7.2 failing to find <zephyr/posix/time.h>
CC: @uLipe

[uLipe]

@pablogs9 , reason and fix here: #390