LibC: add stubs for a lot of functions

libc/unistd.cpp

@@ -0,0 +1,26 @@
+#include <unistd.h>
+
+pid_t fork(void)
+{
+	return -1;
+}
+
+int execv(const char*, char* const[])
+{
+	return -1;
+}
+
+int execve(const char*, char* const[], char* const[])
+{
+	return -1;
+}
+
+int execvp(const char*, char* const[])
+{
+	return -1;
+}
+
+pid_t getpid(void)
+{
+	return -1;
+}