GNU IceCat - Help with Compiler Error on macOS

[saviourms]

I am trying to compile GNU IceCat 60.7.0 on macOS 10.14 following the 
instruction from this outdated guide - 
https://libreplanet.org/wiki/Group:IceCat/Compile_and_package/build_52.6.0_on_macOS
 - and get the following error:

    ....
    checking for c++... /usr/bin/clang++ -std=gnu++14 
    checking whether the C++ compiler (/usr/bin/clang++ -std=gnu++14  ) 
works... no
    configure: error: installation or configuration problem: C++ compiler 
cannot create executables`.
    ....

The config.log says:

    ....
    DEBUG: configure:2292: checking for c++
    DEBUG: configure:2324: checking whether the C++ compiler (/usr/bin/clang++ 
-std=gnu++14  ) works
    DEBUG: configure:2340: /usr/bin/clang++ -std=gnu++14 -o conftest    
conftest.C  1>&5
    DEBUG: clang: warning: libstdc++ is deprecated; move to libc++ with a 
minimum deployment target of OS X 10.9 [-Wdeprecated]
    DEBUG: warning: include path for stdlibc++ headers not found; pass 
'-stdlib=libc++' on the command line to use the libc++ standard library instead 
[-Wstdlibcxx-not-found]
    DEBUG: 1 warning generated.
    DEBUG: ld: library not found for -lstdc++
    DEBUG: clang: error: linker command failed with exit code 1 (use -v to see 
invocation)
    ....

What I've figured out so far is that Apple now doesn't support newer versions 
of libstdc++ and instead wants us to use libc++ (which is supposedly ABI 
compatible with libstdc++). So it helpfully suggests that we set the flag 
'-stdlib=libc++'.

I am stuck here - Where do I make the changes in the build instruction to pass 
this compiler flag? Do I have to modify the autoconf / configure template or 
can I pass this compiler flag to Configure, as an option, when invoking it? A 
little hand holding would be appreciated as I am not really familiar with 
autoconf and working with c++ but am willing to learn. Thanks