make eigen the last blas option (#1025)

Author: borg323

meson.build

@@ -228,12 +228,7 @@ if get_option('build_backends')
   endif
 
   if get_option('blas')
-    if get_option('eigen')
-      add_project_arguments('-DUSE_EIGEN', language : 'cpp')
-      has_blas = true
-      deps += subproject('eigen').get_variable('eigen_dep')
-
-    elif get_option('mkl') and mkl_lib.found()
+    if get_option('mkl') and mkl_lib.found()
       add_project_arguments('-DUSE_MKL', language : 'cpp')
       includes += include_directories(get_option('mkl_include'))
       deps += [ mkl_lib ]
@@ -271,6 +266,11 @@ if get_option('build_backends')
 
       deps += [ openblas_lib ]
       has_blas = true
+
+    elif get_option('eigen')
+      add_project_arguments('-DUSE_EIGEN', language : 'cpp')
+      has_blas = true
+      deps += subproject('eigen').get_variable('eigen_dep')
     endif
 
     ispc = find_program('ispc', required: false)