Bugfix/c89 compile fixes (#327)

* Fix code to be able to compile with older C89 ANSI compilers

* Convert C++ comments to C89 comments.

* default to std=gnu89

* Fix to enable CMake 3.1 to build on Centos7

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

comment.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# This script converts any C++ comments to C comments
+# using the ccmtcnvt tool from the liwc package
+
+CONVERTER=/usr/bin/ccmtcnvt
+# silent fail if the tool is not installed
+[ -x ${CONVERTER} ] || exit 0
+
+directory=${1-`pwd`}
+for filename in $( find ${directory} -name '*.c' )
+do
+  echo Converting ${filename}
+  TEMPFILE="/tmp/ccmtcnvt.$RANDOM.txt"
+  ${CONVERTER} ${filename} > ${TEMPFILE}
+  mv ${TEMPFILE} ${filename}
+done
+
+for filename in $( find ${directory} -name '*.h' )
+do
+  echo Converting ${filename}
+  TEMPFILE="/tmp/ccmtcnvt.$RANDOM.txt"
+  ${CONVERTER} ${filename} > ${TEMPFILE}
+  mv ${TEMPFILE} ${filename}
+done
+