Fixes #3941: Move r29769 to v1.7 branch (revert Voltaire for relevant folks)

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r29769 [[BR]]
revert Voltaire for relevant folks
cmr=v1.7.4:reviewer=ompi-rm1.7
Fixes #3939: Move fix for static compile of CUDA-aware to 1.7

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r29755 [[BR]]
Call function from function table.  Discovered during static build.
Fixes #3942: Move r29773 to v1.7 branch (fix mca_base_var_source_override test)

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r29773 [[BR]]
Fix conditional: don't just check the constant (thanks to clang for an
excellent warning message!)

cmr=v1.7.4:reviewer=hjelmn:subject=fix MCA_BASE_VAR_SOURCE_OVERRIDE test