[CMake] Error if SOFIE test requirements not found and fail-on-missing

It's not good that we only emit a warning if SOFIE is not tested. Like
this, we risk losing test coverage without us knowing.

Author: guitargeek

cmake/modules/SearchInstalledSoftware.cmake

@@ -1609,7 +1609,11 @@ if(tmva-sofie)
     message(STATUS "Looking for BLAS as an optional testing dependency of TMVA-SOFIE")
     find_package(BLAS)
     if(NOT BLAS_FOUND)
-      message(WARNING "BLAS not found: TMVA-SOFIE will not be fully tested")
+      if(fail-on-missing)
+        message(FATAL_ERROR "BLAS not found, but it's required for TMVA-SOFIE testing")
+      else()
+        message(WARNING "BLAS not found: TMVA-SOFIE will not be fully tested")
+      endif()
     endif()
   endif()
   message(STATUS "Looking for Protobuf")