[cmake] Improve logic when MKL is detected as LAPACK distribution

- If no BLA_VENDOR specified, link against single dynamic library
  and set MKL_INTERFACE_LAYER to GNU,LP64 at runtime

c++/nda/CMakeLists.txt

@@ -46,18 +46,16 @@ target_link_libraries(${PROJECT_NAME}_c PUBLIC OpenMP::OpenMP_CXX)
 
 message(STATUS "-------- Lapack detection -------------")
 
-find_package(LAPACK REQUIRED)
-if(LAPACK_LIBRARIES MATCHES "libmkl" AND NOT LAPACK_LIBRARIES MATCHES "libmkl_rt")
-  message(STATUS "Found MKL: Making sure to use single dynamic library")
+find_package(LAPACK QUIET REQUIRED)
+if(LAPACK_LIBRARIES MATCHES "libmkl" AND BLA_VENDOR STREQUAL "All")
+  message(STATUS "Detected MKL with no BLA_VENDOR set, defaulting to single dynamic library 'libmkl_rt'")
   set(BLA_VENDOR Intel10_64_dyn)
-  find_package(LAPACK REQUIRED)
-endif()
-if(LAPACK_LIBRARIES MATCHES "Accelerate.framework")
-  message(STATUS "Can't build with Accelerate Framework on OSX, trying to find OpenBLAS instead.")
+elseif(LAPACK_LIBRARIES MATCHES "Accelerate.framework")
+  message(STATUS "Can't build with Accelerate Framework on OSX, trying to find OpenBLAS instead...")
   set(BLA_VENDOR OpenBLAS) # Accelerate Framework has issue in zdot
   set(LAPACK_ROOT "${LAPACK_ROOT};$ENV{LAPACK_ROOT};/opt/homebrew/opt/openblas;/usr/local/opt/openblas")
-  find_package(LAPACK REQUIRED)
 endif()
+find_package(LAPACK REQUIRED)
 
 # Create an interface target
 add_library(blas_lapack INTERFACE)
@@ -70,6 +68,9 @@ if(LAPACK_LIBRARIES MATCHES "libmkl")
     target_include_directories(${PROJECT_NAME}_c PUBLIC $ENV{MKLROOT}/include)
   endif()
   target_compile_definitions(${PROJECT_NAME}_c PUBLIC NDA_USE_MKL)
+  if(LAPACK_LIBRARIES MATCHES "libmkl_rt")
+    target_compile_definitions(${PROJECT_NAME}_c PRIVATE NDA_USE_MKL_RT)
+  endif()
 endif()
 
 # Link against interface target and export

c++/nda/blas/interface/cxx_interface.cpp

@@ -29,7 +29,9 @@ using namespace std::string_literals;
 #ifdef NDA_USE_MKL
 #include <mkl.h>
 namespace nda::blas {
+#ifdef NDA_USE_MKL_RT
   static int const mkl_interface_layer = mkl_set_interface_layer(MKL_INTERFACE_LP64 + MKL_INTERFACE_GNU);
+#endif
   inline auto *mklcplx(nda::dcomplex *c) { return reinterpret_cast<MKL_Complex16 *>(c); }               // NOLINT
   inline auto *mklcplx(nda::dcomplex const *c) { return reinterpret_cast<const MKL_Complex16 *>(c); }   // NOLINT
   inline auto *mklcplx(nda::dcomplex **c) { return reinterpret_cast<MKL_Complex16 **>(c); }             // NOLINT