JNI build should use default cmake FindJNI.cmake

From http://mail-archives.apache.org/mod_mbox/hadoop-common-dev/201505.mbox/%3C55568DAC.1040303%40oracle.com%3E
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Why does hadoop-common-project/hadoop-common/src/CMakeLists.txt use JNIFlags.cmake in the same directory to set things up for JNI
compilation rather than FindJNI.cmake, which comes as a standard cmake
module? The checks in JNIFlags.cmake make several assumptions that I
believe are only correct on Linux whereas I'd expect FindJNI.cmake to be
more platform-independent.
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Just checked the repo of cmake and it turns out that FindJNI.cmake is
available even before cmake 2.4. I think it makes sense to file a bug
to replace it to the standard cmake module. Can you please file a jira
for this?
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This also applies to hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-nativetask/src/JNIFlags.cmake