Get rid of EIGEN_TEST_FUNC, unit tests must now be declared with EIGEN_DECLARE_TEST(mytest) { /* code */ }.

This provide several advantages:
- more flexibility in designing unit tests
- unit tests can be glued to speed up compilation
- unit tests are compiled with same predefined macros, which is a requirement for zapcc

test/boostmultiprec.cpp

@@ -145,7 +145,7 @@ namespace Eigen {
 
 }
 
-void test_boostmultiprec()
+EIGEN_DECLARE_TEST(boostmultiprec)
 {
   typedef Matrix<Real,Dynamic,Dynamic> Mat;
   typedef Matrix<std::complex<Real>,Dynamic,Dynamic> MatC;