Fix build when +stratimikos +xpetra (#17971)

If Thyra isn't explicitly enabled at the package level, trilinos fails
to build.

```
/var/folders/gy/mrg1ffts2h945qj9k29s1l1dvvmbqb/T/s3j/spack-stage/spack-stage-trilinos-12.18.1-vfmemkls4ncta6qoptm5s7bcmrxnjhnd/spack-src/packages/muelu/adapters/stratimikos/Thyra_XpetraLinearOp_def.hpp:167:15: error:
      no member named 'ThyraUtils' in namespace 'Xpetra'
      Xpetra::ThyraUtils<Scalar,LocalOrdinal,GlobalOrdinal,Node>::toXpetra(rcpFromRef(X_in), comm);
      ~~~~~~~~^
```

1 files changed, 8 insertions, 0 deletions

diff --git a/var/spack/repos/builtin/packages/trilinos/package.py b/var/spack/repos/builtin/packages/trilinos/package.py
index 259f98785b..2924fd7a38 100644
--- a/var/spack/repos/builtin/packages/trilinos/package.py
+++ b/var/spack/repos/builtin/packages/trilinos/package.py
@@ -245,6 +245,7 @@ class Trilinos(CMakePackage):
     conflicts('+amesos', when='~epetra')
     conflicts('+amesos', when='~teuchos')
     conflicts('+anasazi', when='~teuchos')
+    conflicts('+aztec', when='~epetra')
     conflicts('+belos', when='~teuchos')
     conflicts('+epetraext', when='~epetra')
     conflicts('+epetraext', when='~teuchos')
@@ -515,6 +516,13 @@ class Trilinos(CMakePackage):
             ])
 
         if '+stratimikos' in spec:
+            # Explicitly enable Thyra (ThyraCore is required). If you don't do
+            # this, then you get "NOT setting ${pkg}_ENABLE_Thyra=ON since
+            # Thyra is NOT enabled at this point!" leading to eventual build
+            # errors if using MueLu because `Xpetra_ENABLE_Thyra` is set to
+            # off.
+            options.append(define('Trilinos_ENABLE_Thyra', True))
+
             # Add thyra adapters based on package enables
             options.extend(
                 define_trilinos_enable('Thyra' + pkg + 'Adapters', pkg.lower())