visit package update, add glu as a linux dep (#17537)

* visit: add glu as a dep for linux

* add note to suggested install command about mesa

var/spack/repos/builtin/packages/visit/package.py

@@ -25,6 +25,11 @@ class Visit(CMakePackage):
     # linux:
     #  spack install visit ^python+shared ^glib@2.56.3 ^py-setuptools@44.1.0
     #
+    # linux w/o opengl: (add mesa as opengl if system lacks system opengl )
+    #
+    #  spack install visit ^python+shared ^glib@2.56.3 ^py-setuptools@44.1.0 \
+    #                      ^mesa+opengl
+    #
     # macOS:
     #  spack install visit ^python+shared ^glib@2.56.3 ^py-setuptools@44.1.0 \
     #                      ^qt~framework
@@ -159,6 +164,7 @@ class Visit(CMakePackage):
     # https://github.com/visit-dav/visit/issues/3498
     depends_on('vtk@8.1.0:8.1.999+opengl2~python', when='~python @3.0:3.999,develop')
     depends_on('vtk@8.1.0:8.1.999+opengl2+python', when='+python @3.0:3.999,develop')
+    depends_on('glu', when='platform=linux')
     depends_on('vtk@6.1.0~opengl2', when='@:2.999')
     depends_on('vtk+python', when='+python @3.0:,develop')
     depends_on('vtk~mpi', when='~mpi')