util: move zalloc to util-mem.h

zalloc pre-dates util-mem.h but let's move it there, it makes more sense
than including util-strings.h.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1204>

src/util-mem.h

@@ -26,10 +26,28 @@
 
 #include "config.h"
 
+#include <assert.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
 
+static inline void *
+zalloc(size_t size)
+{
+	void *p;
+
+	/* We never need to alloc anything more than 1,5 MB so we can assume
+	 * if we ever get above that something's going wrong */
+	if (size > 1536 * 1024)
+		assert(!"bug: internal malloc size limit exceeded");
+
+	p = calloc(1, size);
+	if (!p)
+		abort();
+
+	return p;
+}
+
 /**
  * Use: _cleanup_(somefunction) struct foo *bar;
  */

src/util-strings.h

@@ -70,23 +70,6 @@ strneq(const char *str1, const char *str2, int n)
 	return str1 == str2;
 }
 
-static inline void *
-zalloc(size_t size)
-{
-	void *p;
-
-	/* We never need to alloc anything more than 1,5 MB so we can assume
-	 * if we ever get above that something's going wrong */
-	if (size > 1536 * 1024)
-		assert(!"bug: internal malloc size limit exceeded");
-
-	p = calloc(1, size);
-	if (!p)
-		abort();
-
-	return p;
-}
-
 /**
  * strdup guaranteed to succeed. If the input string is NULL, the output
  * string is NULL. If the input string is a string pointer, we strdup or