So that points to you not using the CMake build files. So your first step should be to use cmake to generate appropriate makefiles with CUDA enabled and then use those to make bitcoin.
I tried that at first, but build failed. This is the debug output i got:
bitcoin-svn-rev-158 # make bitcoind
-- Found BerkeleyDB: /usr/lib64/libdb.so
-- Configuring done
-- Generating done
-- Build files have been written to: /home/Bitcoin/bitcoin-svn-rev-158
[ 5%] Building NVCC (Device) object cmake-bitcoind/./bitcoind_generated_bitcoinminercuda.cu.o
Scanning dependencies of target bitcoind
[ 11%] Building CXX object cmake-bitcoind/CMakeFiles/bitcoind.dir/__/src/db.cpp.o
In file included from /home/Bitcoin/bitcoin-svn-rev-158/src/db.cpp:5:
/home/Bitcoin/bitcoin-svn-rev-158/src/headers.h:45:20: error: db_cxx.h: Nie ma takiego pliku ani katalogu
In file included from /home/Bitcoin/bitcoin-svn-rev-158/src/headers.h:123,
from /home/Bitcoin/bitcoin-svn-rev-158/src/db.cpp:5:
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:26: error: DbEnv does not name a type
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:37: error: ISO C++ forbids declaration of Db with no type
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:37: error: expected ; before * token
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:39: error: DbTxn was not declared in this scope
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:39: error: template argument 1 is invalid
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:39: error: template argument 2 is invalid
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:152: error: ISO C++ forbids declaration of Dbc with no type
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:152: error: expected ; before * token
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:163: error: expected `;' before int
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:163: error: Dbc has not been declared
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:202: error: ISO C++ forbids declaration of DbTxn with no type
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:202: error: expected ; before * token
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:210: error: expected `;' before public
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:163: error: DB_NEXT was not declared in this scope
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h: In member function bool CDB::Read(const K&, T&):
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:54: error: pdb was not declared in this scope
/home/Bitcoin/bitcoin-svn-rev-158/src/db.h:61: error: Dbt was not declared in this scope
(...)
(...)
However that approach won't work with Gentoo ebuild/emerge system, so i abandoned it.
Seems the the db include directory was not set correctly. Can you search your system for db_cxx.h and db.h and post the results? I'll try to look at it when I have time.