Release 1.3.1; Require C++17, lttoolbox 3.7.1

configure.ac

@@ -15,7 +15,7 @@ AC_ARG_ENABLE(debug,
               [  --enable-debug  Enable "-g" compiler options],
               [CXXFLAGS="-g $CXXFLAGS";CFLAGS="-g $CFLAGS"])
 
-PKG_CHECK_MODULES([LTTOOLBOX], [lttoolbox >= 3.6.0])
+PKG_CHECK_MODULES([LTTOOLBOX], [lttoolbox >= 3.7.1])
 PKG_CHECK_MODULES([ICU_UC], [icu-uc])
 PKG_CHECK_MODULES([ICU_IO], [icu-io])
 
@@ -26,12 +26,12 @@ LIBS="$LIBS $LTTOOLBOX_LIBS $ICU_LIBS $ICU_UC_LIBS $ICU_IO_LIBS"
 
 # Checks for highest supported C++ standard
 AC_LANG(C++)
-for version in 23 2b 20 2a 17 1z 14 1y; do
+for version in 23 2b 20 2a 17; do
   version_flag="-std=c++${version}"
   AX_CHECK_COMPILE_FLAG([${version_flag}], [break], [version_flag=none])
 done
 AS_IF([test "$version_flag" == none], [
-  AC_MSG_ERROR([Could not enable at least C++1y (C++14) - upgrade your compiler])
+  AC_MSG_ERROR([Could not enable at least C++17 - upgrade your compiler])
 ])
 CXXFLAGS="$CXXFLAGS ${version_flag}"