The toolchain is complaining about not being able to find the header files. Did you modify any project settings or so? I mean, the default application template works fine for me so it seems something might be modified on your side.
I cannot see the build command on your console window but it should look like bellow:
'Invoking: ARM v7 Linux g++ linker'
arm-linux-gnueabihf-g++ -L"C:\Xilinx\SDK\2018.3\data\embeddedsw\ThirdParty\opencv\aarch32\lib" -o "test.elf" ./src/main.o -lopencv_core
Ibai Don’t forget to reply, kudo, and accept as solution.