Q:

I'm trying to compile bitcoind on Windows but build_unix for db-4.8.30.NC is empty.  What do I need to do? 

I've been working on setting up the proper environment to compile litecoin, and have been following the instructions from this:
https://bitcointalk.org/index.php?PHPSESSID=1dl8pkva2oqpjsd3h455k7hrj7&topic=149479.0;all

2.2 Berkeley DB: http://download.oracle.com/berkeley-db/db-4.8.30.NC.tar.gz
We'll use version 4.8 to preserve binary wallet compatibility. 
From a MinGW shell unpack the source archive, configure, edit line 113 of db.h then make:
Code:

cd /c/deps/

tar xvfz db-4.8.30.NC.tar.gz

cd db-4.8.30.NC/build_unix

../dist/configure --disable-replication --enable-mingw --enable-cxx

after configuring make sure to edit your build_unix/db.h by replacing line 113:
Code:

typedef pthread_t db_threadid_t;

with
Code:

typedef u_int32_t db_threadid_t;

I was all set to do it, but this happened:

I've tried getting db-4.8.30.NC from multiple sources, but no luck—the build_unix folder is always empty. 
So what's the deal? 

A:

The build_unix directory contains just the .IGNORE_ME file in the distribution.   The directory is populated by the make command. 
../dist/configure --disable-replication --enable-mingw --enable-cxx
make

You do not need to edit db.h in the latest distribution since they have already corrected the typedef.