The following in config.log shows why:
configure:27774: checking for compiler familyid
configure:27804: xlc -o conftest -q64 -g -I/home/hargrove/SCRATCH/OMPI/openmpi-1.7-latest-linux-ppc64-xlc-12.1/openmpi-1.7.4rc2r30303/ompi/include conftest.c >&5
"conftest.c", line 190.10: 1506-296 (S) #include file "mpi_portable_platform.h" not found.
"conftest.c", line 197.23: 1506-045 (S) Undeclared identifier PLATFORM_COMPILER_FAMILYID.
configure:27804: $? = 1
configure: program exited with status 1
$ tar tvfj openmpi-1.7.4rc2r30303.tar.bz2 | grep portable_platform
-rw-r--r-- mpiteam/projects 16055 2014-01-17 02:33 openmpi-1.7.4rc2r30303/opal/include/opal/opal_portable_platform.h
So, it appears the probe for compiler family didn't keep up with the change in name and location of the portable_platform header (r29618).
Inspection of my tests on both v1.7 and trunk seems to show the same issue in both.
The attached patch is an untested shot at fixing the problem.
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