5a, 5c, 6a, 6c, 8a, 8c: fix Windows file paths

Verified with objdump -W.

R=alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/4974061
diff --git a/include/libc.h b/include/libc.h
index 0817d77..f9ad963 100644
--- a/include/libc.h
+++ b/include/libc.h
@@ -307,6 +307,8 @@
 extern int fork(void);
 extern int pread(int fd, void *buf, int n, int off);
 extern int pwrite(int fd, void *buf, int n, int off);
+#undef  getwd
+#define getwd(s, ns) getcwd(s, ns)
 #undef  lseek
 #define lseek(fd, n, base) _lseeki64(fd, n, base)
 #define mkdir(path, perm) mkdir(path)