Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -170,6 +170,12 @@
 set(CMAKE_EXE_LINKER_FLAGS
     "${CMAKE_EXE_LINKER_FLAGS} ${TEST_SUITE_EXTRA_EXE_LINKER_FLAGS}")
 
+# Use X/OPEN compatibility flag on AIX for C tests to avoid problems
+# with some versions of the system headers.
+if(CMAKE_SYSTEM_NAME STREQUAL "AIX")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_XOPEN_SOURCE=700")
+endif()
+
 # This is either directly the C++ ABI library or the full C++ library
 # which pulls in the ABI transitively.
 set(TEST_SUITE_CXX_ABI "default" CACHE STRING "Specify C++ ABI library to use.")
Index: MultiSource/Benchmarks/DOE-ProxyApps-C++/miniFE/CMakeLists.txt
===================================================================
--- MultiSource/Benchmarks/DOE-ProxyApps-C++/miniFE/CMakeLists.txt
+++ MultiSource/Benchmarks/DOE-ProxyApps-C++/miniFE/CMakeLists.txt
@@ -1,4 +1,4 @@
-list(APPEND CXXFLAGS -I. -DMINIFE_SCALAR=double  -DMINIFE_LOCAL_ORDINAL=int -DMINIFE_GLOBAL_ORDINAL=int -DMINIFE_CSR_MATRIX -DREDSTORM) # -DREDSTORM for mkdir
+list(APPEND CXXFLAGS -I. -DMINIFE_SCALAR=double  -DMINIFE_LOCAL_ORDINAL=int -DMINIFE_GLOBAL_ORDINAL=int -DMINIFE_CSR_MATRIX -DREDSTORM -D_XOPEN_SOURCE=700) # -DREDSTORM for mkdir
 list(APPEND LDFLAGS -lm)
 set(RUN_OPTIONS -nx 64 -ny 64 -nz 64)
 llvm_multisource(miniFE)