xSDKTrilinos build fails on Mac due to excessively long command line generated by cmake

[BarrySmith]

The xSDKTrilinos cmake is stacking about 100 copies of the xSDKTrilinos_EXTRA_LINK_FLAGS= at the end of its link line for shared libraries. Maybe it stacks one for each Trilinos library it is linking against.

This results in a huge command line which is more than the shell can handle so the link fails.

Somehow the xSDKTrilinos_EXTRA_LINK_FLAGS value needs to be handled in a smarter way so only one is used independent of how many Trilinos libraries it is linking against.

Note that Trilinos cmake is also occassionally stacking several of these together but never enough to crash the shell.

Attached is all the info we can gather from the xSDKTrilinos build process.
xsdktrilinos.txt

@amklinv @jwillenbring @bartlettroscoe @balay