Eigen: move C API into intern/eigen.

build_files/cmake/cmake_consistency_check_config.py

build_files/cmake/macros.cmake

extern/CMakeLists.txt

extern/SConscript

intern/CMakeLists.txt

intern/SConscript

intern/eigen/CMakeLists.txt

intern/eigen/SConscript

intern/eigen/eigen_capi.h

intern/eigen/intern/eigenvalues.cc

intern/eigen/intern/eigenvalues.h

intern/eigen/intern/svd.cc

intern/eigen/intern/svd.h

source/blender/blenlib/CMakeLists.txt

source/blender/blenlib/SConscript

source/blender/blenlib/intern/math_solvers.c

source/blender/physics/CMakeLists.txt

source/blenderplayer/CMakeLists.txt

tests/gtests/blenlib/CMakeLists.txt