libtool uses cc to link a mixed C/C++ project and fails to find operator new

[Yuri]

On FreeBSD libtool can't find operator new[] because it is in C mode:

libtool: link: cc -fno-strict-aliasing -fopenmp -ftree-vectorize 
-pthread -O2 -pipe -fno-omit-frame-pointer -fstack-protector-strong 
-fno-strict-aliasing -fno-strict-aliasing -fstack-protector-strong -o 
RNALfold RNALfold_cmdl.o RNALfold.o 
../../src/ViennaRNA/.libs/libRNA_conv.a ./.libs/libhelpers.a -lm 
-pthread -fopenmp
libtool: link: cc -fno-strict-aliasing -fopenmp -ftree-vectorize 
-pthread -O2 -pipe -fno-omit-frame-pointer -fstack-protector-strong 
-fno-strict-aliasing -fno-strict-aliasing -fstack-protector-strong -o 
RNALalifold RNALalifold_cmdl.o RNALalifold.o  
../../src/ViennaRNA/.libs/libRNA_conv.a ./.libs/libhelpers.a -lm 
-pthread -fopenmp
ld: error: undefined symbol: operator new[](unsigned long)
>>> referenced by svm.cpp
>>>               svm.o:(Kernel::Kernel(int, svm_node* const*, 
svm_parameter const&)) in archive ../../src/ViennaRNA/.libs/libRNA_conv.a



I added "LT_LANG([C++]) to configure.ac but it didn't help:

AC_PROG_LIBTOOL
LT_INIT([pic-only, static])
LT_LANG([C++])
AC_SUBST(LIBTOOL_DEPS)


How to switch libtool to the C++ mode?


The source tarball: 
https://www.tbi.univie.ac.at/RNA/download/sourcecode/2_4_x/ViennaRNA-2.4.13.tar.gz


Thank you,

Yuri