Typo-fixes and a rephrase in HACKING.md

s/absued/abused/
s/indenpendent/independent/
Rewrote garbled line about keeping log messages atomic.

(cherry picked from commit 65044bd284dcf863692198276db0ffcb3711df49)
Add xasprintf() to the suggested alternatives, it can replace the malloc()+sprintf() idiom.

(cherry picked from commit c7fcb08ae423c4e8c3022c84e2580e61ab1e0473)
Redmine 6225: Disable examples checking on non-Linux platforms.

(cherry picked from commit 9157bd8cf063058811cd3f8fd8a5c8900732b764)
Correct copy-paste error in README.

(cherry picked from commit d4f16c6abbb7c2a07eea51e6c04b98a16cda4af4)
Add clarifying comment to endif.

(cherry picked from commit 03bde26c777f07532c05fcabb38516be15dbbc8c)