--- gdb-7.6.2.org/gdb/common/linux-ptrace.h
+++ gdb-7.6.2/gdb/common/linux-ptrace.h
@@ -67,6 +67,7 @@
 #define __WALL          0x40000000 /* Wait for any child.  */
 #endif
 
+#include <unistd.h> /* for pid_t */
 extern void linux_ptrace_attach_warnings (pid_t pid, struct buffer *buffer);
 extern void linux_ptrace_init_warnings (void);