Check if a preprocessor variable is defined before use.
Check if a preprocessor variable is defined before use.

Clang complains about this with -Wundef on.

sairajat/dealii,kalj/dealii,naliboff/dealii,sairajat/dealii,sairajat/dealii,naliboff/dealii,naliboff/dealii,kalj/dealii,naliboff/dealii,EGP-CIG-REU/dealii,danshapero/dealii,kalj/dealii,kalj/dealii,kalj/dealii,EGP-CIG-REU/dealii,EGP-CIG-REU/dealii,EGP-CIG-REU/dealii,naliboff/dealii,kalj/dealii,danshapero/dealii,danshapero/dealii,EGP-CIG-REU/dealii,EGP-CIG-REU/dealii,naliboff/dealii,sairajat/dealii,EGP-CIG-REU/dealii,sairajat/dealii,danshapero/dealii,sairajat/dealii,danshapero/dealii,naliboff/dealii,kalj/dealii,sairajat/dealii,danshapero/dealii,danshapero/dealii