MueLu: Xpetra: fix macro usage in cmake files
This commit allows the MueLu TwoBillion test to compile and run nontrivially again. There were multiple problems: 1) The TwoBillion test itself was using an Xpetra preprocessor macro that wasn't ever defined. 2) The TwoBillion test was protected in CMake with an Xpetra variable that was set with "SET" instead of "SET_GLOBAL". 3) MueLu wasn't using the ASSERT_DEFINED cmake macro, which throws an error if a variable isn't defined and would have caught issue #2. Build/Test Cases Summary Enabled Packages: MueLu, Xpetra Enabled all Forward Packages 0) MPI_DEBUG => passed: passed=356,notpassed=0 (27.99 min) 1) SERIAL_RELEASE => passed: passed=348,notpassed=0 (15.15 min) 2) MPI_SS_DEBUG => FAILED: passed=619,notpassed=2 => Not ready to push! (54.96 min) 3) SERIAL_SS_RELEASE => passed: passed=354,notpassed=0 (26.55 min) WARNING: Forced the push!