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

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

	$ cat ~/tmp/spatch/streq.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/streq.sp;

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

lib/limits.c

@@ -413,9 +413,9 @@ static int setup_user_limits (const char *uname)
 		}
 	}
 	(void) fclose (fil);
-	if (limits[0] == '\0') {
+	if (streq(limits, "")) {
 		/* no user specific limits */
-		if (deflimits[0] == '\0') {	/* no default limits */
+		if (streq(deflimits, "")) {	/* no default limits */
 			return 0;
 		}
 		strcpy (limits, deflimits);	/* use the default limits */