Support for VxWorks in curl was added by the community in 2009. This code hadn’t been updated in a while so it was removed as part of routine maintenance work: https://github.com/curl/curl/pull/8362
Here are the instructions for building the latest curl from git using the VxWorks SDK:
Create a new project directory
mkdir $HOME/curltest
cd $HOME/curltest
Source the SDK environment
source /opt/wrsdk/wrsdk-vxworks7-qemu/toolkit/wind_sdk_env.linux
Clone the git repository
git clone https://github.com/curl/curl.git
Change directories
cd curl
Create the configure script
autoreconf -fi
Configure the Makefile for cross-building for VxWorks with the SDK
ac_cv_header_termios_h=no ./configure --build=x86_64-pc-linux-gnu --host=x86_64-wrs-vxworks --disable-ntlm-wb --with-openssl
Build curl
make
Export the libraries, executables, and headers into a directory
mkdir $TMPDIR/vxworks
DESTDIR=$TMPDIR/vxworks make install