Set HAVE_<PACKAGE_NAME_UC>_<UPSTREAM_PACKAGE_NAME_UC>=OFF for missing…

…/undefined packages (TriBITSPub#63)

This is a better solution to the failure reported in trilinos/Trilinos#12291
and applied in the reverted commit:

  05d4429 "Only assert defined vars conditionally"
  Author: Samuel Browne <[email protected]>
  Date:   Thu Sep 28 13:51:05 2023 -0600 (6 days ago)

(which I had suggested at the time).

This new implementation sets
HAVE_<PACKAGE_NAME_UC>_<UPSTREAM_PACKAGE_NAME_UC>=OFF at the project level
right away when the dependencies are being read in and <upstreamPackageName>
is not defined.  This makes for more robust downstream CMake code that works
with optional upstream dependencies when those dependencies are not defined
(like when the package <upstreamPackageName> was removed from the reduced
source tree by the reduced tarball feature).  A downstream package should not
care whether an upstream dependence is disabled or is missing entirely; the
reaction should be the same and it should be able to rely on the same
variables.

tribits/core/package_arch/TribitsReadDepsFilesCreateDepsGraph.cmake

@@ -39,6 +39,8 @@
 
 include(TribitsPackageDefineDependencies)
 include(TribitsPackageDependencies)
+include(TribitsGetHavePackageDependencyMacroName)
+
 include(SetDefault)
 include(DualScopeSet)
 
@@ -553,11 +555,6 @@ endfunction()
 # Implementation macro for tribits_set_dep_packages() to deal with a package
 # that is not defined by TriBITS.
 #
-# ToDo #63: This may need to be modified when dealing with TriBITS-compliant
-# packages already installed out on the system.  We may need a mode where we
-# don't assert packages that are not defined but instead just assume they are
-# TriBITS-compliant packages already installed.
-#
 macro(tribits_set_dep_packages__handle_undefined_pkg  packageName  depPkg
     requiredOrOptional  pkgsOrTpls  packageEnableVar
   )
@@ -592,6 +589,9 @@ macro(tribits_set_dep_packages__handle_undefined_pkg  packageName  depPkg
     # work.
     set(${PROJECT_NAME}_ENABLE_${depPkg} OFF)
     set(${packageName}_ENABLE_${depPkg} OFF)
+    tribits_get_have_package_dependency_macro_name(${packageName} ${depPkg}
+      havePackageDepPkgMacroName)
+    set(${havePackageDepPkgMacroName} OFF)
   endif()
 endmacro()