[beast: 1/4] BUILD: configure.ac: compile as C++-14 code, depend on g++-5.2.1

[Tim Janik <timj src gnome org>]

commit d97b0d96d8253d51a2cbe0cf6b9322a8ef22e2e4
Author: Tim Janik <timj gnu org>
Date:   Sun Sep 10 21:12:13 2017 +0200

    BUILD: configure.ac: compile as C++-14 code, depend on g++-5.2.1
    
    Signed-off-by: Tim Janik <timj gnu org>

 configure.ac |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 2803c18..8d7089e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -147,11 +147,11 @@ AC_DEFINE_UNQUOTED(CONFIGURE_INSTALLPATH_OBJDIR, [".libs"], [Directory used for
 AC_LIBTOOL_DLOPEN
 
 # == C++ Dialect ==
-CXX="$CXX -std=gnu++11"
-test -z "$CXXCPP" || CXXCPP="$CXXCPP -std=gnu++11"
+CXX="$CXX -std=gnu++14"
+test -z "$CXXCPP" || CXXCPP="$CXXCPP -std=gnu++14"
 
 # == Compiler flags ==
-# needs gcc >= 4.8, clang >= 3.4
+# needs gcc >= 5, clang >= 3.4
 c_warnings="-Wall -Wdeprecated -Werror=format-security -Wredundant-decls -Wpointer-arith 
-Wmissing-declarations" # -Wdate-time -Wconversion -Wshadow
 cxx_warnings="-Wsign-promo -Woverloaded-virtual" # -Wnon-virtual-dtor  -Wempty-body -Wignored-qualifiers 
-Wunreachable-code -Wtype-limits
 c_only_flags="-Wmissing-prototypes -Wnested-externs -Wno-pointer-sign"
@@ -172,17 +172,17 @@ x86_64_flags="-mcx16"                             # for CMPXCHG16B, in AMD64 since 2005
 #x86_64_flags="$x86_64_flags -mavx"            # Intel since 2011, AMD since 2011
 #x86_64_flags="$x86_64_flags -mavx2"           # Intel since 2013, AMD since 2015
 AC_MSG_CHECKING([for known C++ compiler])
-if   ${CXX} --version 2>&1 | grep -q -F 'clang' ; then
+if   ${CXX} --version 2>&1 | grep -q -F 'clang' ; then # clang
     AC_MSG_RESULT([clang++])
     AM_CFLAGS="$c_warnings $c_only_flags $compiler_flags $optimization_flags $clang_fix_flags"
     AM_CXXFLAGS="$c_warnings $cxx_warnings $compiler_flags $optimization_flags $clang_fix_flags"
     MC_ASSERT_VERSION($CXX --version, 3.5.0)
-elif ${CXX} --version 2>&1 | grep -q -E 'Free Software Foundation' ; then
+elif ${CXX} --version 2>&1 | grep -q -E 'Free Software Foundation' ; then # gcc
     AC_MSG_RESULT([g++])
     AM_CFLAGS="$c_warnings $c_only_flags $gcc_c_only_flags $compiler_flags $optimization_flags $gcc_flags"
     AM_CXXFLAGS="$c_warnings $cxx_warnings $compiler_flags $optimization_flags $gcc_flags"
     FAST_MATH_FLAGS="$FAST_MATH_FLAGS $gcc_fast_math"
-    MC_ASSERT_VERSION($CXX --version, 4.9.2)
+    MC_ASSERT_VERSION($CXX --version, 5.2.1)
 else
   AC_MSG_RESULT([none])
   AC_MSG_ERROR([unknown C++ compiler])