building zstd with cmake

[stumbles]

I decided to switch to a cmake build because the meson method didn't/doesn't install the various *cmake configuration files.

These are the switches I used to compile it;

`cd build/cmake

export CFLAGS+=' -ffat-lto-objects'
export CXXFLAGS+=' -ffat-lto-objects'

OPTS+=" -DCMAKE_BUILD_TYPE=Release
-DCMAKE_INSTALL_PREFIX=/usr
-DCMAKE_INSTALL_LIBDIR=lib
-DZSTD_ZLIB_SUPPORT=ON
-DZSTD_LZ4_SUPPORT=ON
-DZSTD_BUILD_CONTRIB=ON
-DZSTD_BUILD_STATIC=OFF
-DZSTD_BUILD_TESTS=ON
-DBUILD_SHARED_LIBS=ON
-DZSTD_PROGRAMS_LINK_SHARED=ON
-DZSTD_BUILD_DEPRECATED=ON
-Wno-dev"

cmake -B zstd-1.5.7 S . -G Ninja $OPTS &&
cmake --build zstd-1.5.7 &&

cmake --install zstd-1.5.7`

It compiles and installs fine. The issue are the cmake files installed in /usr/lib/cmake/zstd/.

I didn't encounter a problem until compiling qttools-everywhere-src-6.9.2 which fails with zstd detection of shared libs;

`CMake Error at /usr/lib64/cmake/zstd/zstdTargets.cmake:42 (message):
Some (but not all) targets in this export set were already defined.

Targets Defined: zstd::libzstd_shared

Targets not yet defined: zstd::libzstd

Call Stack (most recent call first):
/usr/lib64/cmake/zstd/zstdConfig.cmake:42 (include)
/usr/lib/qt6/cmake/Qt6/FindWrapZSTD.cmake:24 (find_package)
/usr/lib/qt6/cmake/Qt6/QtFindPackageHelpers.cmake:141 (find_package)
src/designer/src/lib/CMakeLists.txt:425 (qt_find_package)
`

I get the same issue trying with qttools-everywhere-src-6.9.1. Prior to this and using the meson build or make makefile there were no problems. In those cases qttools just ignores the absence of any cmake config/helper files and moves on.