Fixes for building on FreeBSD and other platforms

FreeBSD current status:
Basilisk II: Builds and runs successfully using gcc and gmake
SheepShaver: Doesn't work because FreeBSD doesn't support mapping
the zero memory page. SheepShaver would only work on *BSD if the
direct addressing mode worked.

BasiliskII/src/Unix/sysdeps.h

@@ -42,6 +42,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <errno.h>
 
 #ifdef HAVE_PTHREADS
 # include <pthread.h>

SheepShaver/src/Unix/sysdeps.h

@@ -44,6 +44,7 @@
 #include <stddef.h>
 #include <string.h>
 #include <signal.h>
+#include <errno.h>
 
 #ifdef HAVE_PTHREADS
 # include <pthread.h>
@@ -170,6 +171,9 @@ typedef int64 intptr;
 #else
 #error "Unsupported size of pointer"
 #endif
+#ifndef HAVE_LOFF_T
+#define loff_t off_t
+#endif
 
 // Define if the host processor supports fast unaligned load/stores
 #if defined __i386__ || defined __x86_64__