lib/, src/: Use !streq() instead of its pattern

lib/, src/: Use !streq() instead of its pattern

Except for the added (and sorted) includes, the removal of redundant
parentheses, and a few non-string cases that I've left out of the
change, this patch can be approximated with the following semantic
patch:

	$ cat ~/tmp/spatch/strneq.sp
	@@
	expression s;
	@@

	- '\0' != *s
	+ !streq(s, "")

	@@
	expression s;
	@@

	- '\0' != s[0]
	+ !streq(s, "")

	@@
	expression s;
	@@

	- *s != '\0'
	+ !streq(s, "")

	@@
	expression s;
	@@

	- s[0] != '\0'
	+ !streq(s, "")

	$ find contrib/ lib* src/ -type f \
	| xargs spatch --in-place --sp-file ~/tmp/spatch/strneq.sp;

Signed-off-by: Alejandro Colomar <alx@kernel.org>