compat: Fix clang compiler error in Android

This includes some missing headers and function declaration and fixes
the following compiler errors.

../compat/htonll.c:27:9: error: call to undeclared function 'htonl'
   27 |     b = htonl (v & 0xffffffff);
      |         ^

../compat/ntohll.c:27:9: error: call to undeclared function 'ntohl'
   27 |     b = ntohl (v & 0xffffffff);
      |         ^

../compat/setproctitle.c:39:47: error: call to undeclared function 'getprogname'
   39 |         used = snprintf(name, sizeof name, "%s: %s", getprogname(), title);
      |                                                      ^

../compat/imsg.c:82:9: error: call to undeclared function 'getdtablesize'
   82 |             >= getdtablesize()) {
      |                ^

compat.h

@@ -289,6 +289,11 @@ void		 explicit_bzero(void *, size_t);
 int		 getdtablecount(void);
 #endif
 
+#ifndef HAVE_GETDTABLESIZE
+/* getdtablesize.c */
+int		 getdtablesize(void);
+#endif
+
 #ifndef HAVE_CLOSEFROM
 /* closefrom.c */
 void		 closefrom(int);

compat/htonll.c

@@ -14,6 +14,7 @@
  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <arpa/inet.h>
 #include <sys/types.h>
 
 #include "compat.h"

compat/ntohll.c

@@ -14,6 +14,7 @@
  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <arpa/inet.h>
 #include <sys/types.h>
 
 #include "compat.h"

compat/setproctitle.c

@@ -17,6 +17,7 @@
 #include <sys/types.h>
 
 #include <stdarg.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include "compat.h"