Build system fixes / improvements

[nebw]

I wasn't able to build cgt on my system, so I had to make a couple of modifications to the CMake script:

• I already have OpenBLAS installed. I such a case, cgt should not download and compile OpenBLAS. I added FindOpenBLAS.cmake from the caffe repository and modified the CMake script so that OpenBLAS is only built from scratch if FindOpenBLAS.cmake can't find OpenBLAS on the system
• appending to CMAKE_C_FLAGS/CMAKE_CXX_FLAGS broke the build on my system because it adds a ';' before appending the string. According to the CMake docs, APPEND is meant for lists (not strings), which are sepearted by semicolons in CMake.

[f0k]

👍