Fix issue where functions are undefined in GCC 15.1

[axelhj]

I was compiling the project on Windows with MSYS2. To extract the tar.gz I used

#!env sh
ID="main"
curl -sL "https://github.com/st3w/neo/archive/${ID}.tar.gz > neo-${ID}.tar.gz"
# Need to extract the file but tar does not handle the symlink/hardlink well.
tar xzf ./neo-${ID}.tar.gz `tar tzf ./neo-${ID}.tar.gz | sed -e '/COPYING/d' | tr "\n" " "`
./autogen.sh
./configure
make
make install # Windows does not have sudo

At that point I got a compilation error because getline wanted to be called with a string stream and strcasestr did not exist (it only exists as some kind of compiler extension). I made 3 small changes and then the compilation worked fine. Not sure if the changes are proper but the executable worked nicely on my system. Thanks for a cool project by the way.