Configure quantlib-config from CMake

[kohnech]

Building QL-SWIG requires that QuantLib was built via autotools and not CMake since
quantlib-config is missing.

How to reproduce:

1. Configure/Build QuantLib via CMake, for example:

cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=../install -DBUILD_SHARED_LIBS=NO ..
cmake --build .

2. Install QuantLib (path installation)
   cmake --install .
3. Configure SWIG and build SWIG (Add QL to PATH):

./autogen.sh
./configure --disable-static --disable-test-suite --enable-unity-build CXXFLAGS="-O3 -g0"
make -C Python 

Error:
/bin/sh: 1: quantlib-config: not found

Since we wanna rely on CMake in our pipelines we prefer adding quantlib-config
build product to CMake which is this PR.

Thank you!
Christian

[boring-cyborg]

Thanks for opening this pull request! It might take a while before we look at it, so don't worry if there seems to be no feedback. We'll get to it.

[CLAassistant]

All committers have signed the CLA.

[lballabio]

Thanks! May you check the CLAassistant comment above?

[coveralls]

Coverage: 71.955%. Remained the same when pulling d17122e on Model-Validation:add_quantlib_config_via_cmake into d6896cb on lballabio:master.

[boring-cyborg]

Congratulations on your first merged pull request!