OpenMP 4.0 in GCC: offload to nVidia GPU

TL;DR - Does GCC (trunk) already support OpenMP 4.0 offloading to nVidia GPU?

If so, what am I doing wrong? (description below).

I'm running Ubuntu 14.04.2 LTS.

I have checked out the most recent GCC trunk (dated 25 Mar 2015).

I have installed the CUDA 7.0 toolkit according to Getting Started on Ubuntu guide. CUDA samples run successfully, i.e. deviceQuery detects my GeForce GT 730.

I have followed the instructions from https://gcc.gnu.org/wiki/Offloading as well as https://gcc.gnu.org/install/specific.html#nvptx-x-none

I have installed nvptx-tools and nvptx-newlib (configure, make, sudo make install), newlib also linked inside GCC's trunk directory with ln -s.

Then I built the target accelerator nvptx-none compiler:

../../trunk/configure --target=nvptx-none --enable-as-accelerator-for=x86_64-pc-linux-gnu --with-build-time-tools=/usr/local/nvptx-none/bin --disable-sjlj-exceptions --enable-newlib-io-long-long
make -j 9
sudo make install DESTDIR=/install

...and the host GCC compiler itself:

../trunk/configure --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu --enable-offload-targets=nvptx-none=/install/prefix --with-cuda-driver=/usr/local/cuda --enable-languages=c,c++
make -j 9
sudo make install DESTDIR=/install

I have set the LD_LIBRARY_PATH accordingly:

export LD_LIBRARY_PATH=/install/usr/local/lib64:/install/usr/local/lib/gcc/nvptx-none/5.0.0/:/usr/local/cuda/lib64:$LD_LIBRARY_PATH

For sure, the mkoffload tool is built:

/install/usr/local/libexec/gcc/x86_64-pc-linux-gnu/5.0.0/accel/nvptx-none/mkoffload

as well the target and host compilers are there:

/install/usr/local/bin/x86_64-pc-linux-gnu-gcc
/install/usr/local/bin/x86_64-pc-linux-gnu-accel-nvptx-none-gcc

But when I compile a sample code that queries the number of devices with omp_get_num_devices(), I get the response 0:

$ /install/usr/local/bin/x86_64-pc-linux-gnu-gcc -fopenmp -foffload=nvptx-none main.c
$ ./a.out
0

When I add -v (verbose) option to the target compiler's options, I get the following output:

$ /install/usr/local/bin/x86_64-pc-linux-gnu-gcc -fopenmp -foffload=nvptx-none="-v" main.c

Using built-in specs.
COLLECT_GCC=/install/usr/local/bin/x86_64-pc-linux-gnu-accel-nvptx-none-gcc
Target: nvptx-none
Configured with: ../../trunk/configure --target=nvptx-none --enable-as-accelerator-for=x86_64-pc-linux-gnu --with-build-time-tools=/usr/local/nvptx-none/bin --disable-sjlj-exceptions --enable-newlib-io-long-long
Thread model: single
gcc version 5.0.0 20150325 (experimental) (GCC) 
COLLECT_GCC_OPTIONS='-m64''-S''-fmath-errno''-fsigned-zeros''-ftrapping-math''-fno-trapv''-fno-strict-overflow''-fno-openacc''-foffload-abi=lp64''-fopenmp''-v''-v''-o''/tmp/cccxIggp.mkoffload'
 /install/usr/local/bin/../libexec/gcc/x86_64-pc-linux-gnu/5.0.0/accel/nvptx-none/lto1 -quiet -dumpbase ccKOW9hi.o -m64 -auxbase-strip /tmp/cccxIggp.mkoffload -version -fmath-errno -fsigned-zeros -ftrapping-math -fno-trapv -fno-strict-overflow -fno-openacc -foffload-abi=lp64 -fopenmp -o /tmp/cccxIggp.mkoffload @/tmp/ccjRDWhp
GNU GIMPLE (GCC) version 5.0.0 20150325 (experimental) (nvptx-none)
    compiled by GNU C version 5.0.0 20150325 (experimental), GMP version 5.1.3, MPFR version 3.1.2-p3, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU GIMPLE (GCC) version 5.0.0 20150325 (experimental) (nvptx-none)
    compiled by GNU C version 5.0.0 20150325 (experimental), GMP version 5.1.3, MPFR version 3.1.2-p3, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
COMPILER_PATH=/install/usr/local/bin/../libexec/gcc/x86_64-pc-linux-gnu/5.0.0/accel/nvptx-none/:/install/usr/local/bin/../libexec/gcc/
LIBRARY_PATH=/install/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/5.0.0/accel/nvptx-none/:/install/usr/local/bin/../lib/gcc/
COLLECT_GCC_OPTIONS='-m64''-S''-fmath-errno''-fsigned-zeros''-ftrapping-math''-fno-trapv''-fno-strict-overflow''-fno-openacc''-foffload-abi=lp64''-fopenmp''-v''-v''-o''/tmp/cccxIggp.mkoffload'

So it looks that the toolchain gets invoked and .mkoffload files are created.

Please help. If it should work, how can I diagnose what's wrong?