MAPREDUCE-6459. Native task crashes when merging spilled file on ppc64. Contributed by Tao Jie and Ayappan.

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-nativetask/src/CMakeLists.txt

@@ -26,7 +26,7 @@ set(GTEST_SRC_DIR ${CMAKE_SOURCE_DIR}/../../../../hadoop-common-project/hadoop-c
 
 # Add extra compiler and linker flags.
 # -Wno-sign-compare
-hadoop_add_compiler_flags("-DNDEBUG -DSIMPLE_MEMCPY -fno-strict-aliasing")
+hadoop_add_compiler_flags("-DNDEBUG -DSIMPLE_MEMCPY -fno-strict-aliasing -fsigned-char")
 
 # Source location.
 set(SRC main/native)