* fix#1111 errno command edge case
This commit fixes the case when errno command causes a binary to
segfault when the `__errno_location` symbol was defined but its .plt.got
entry was not filled yet by the dynamic loader (ld.so), so e.g. when the
glibc library was not loaded yet.
In such a case, us triggering a call to `__errno_location` function
triggered a jump to an unmapped address. Now, we dereference that
.plt.got symbol and see if it lives in mapped memory.
* add tip about errno command
* errno: fix case when __errno_location@got.plt is missing
* fix lint
* fix sh lint
* fix errno test
Filip Mazur