qbspkgconfig generated wrong link order when merging dependencies

When merging dependencies by setting "qbspkgconfig.mergeDependencies: true" (which is the default) the link order might get scrambled.

I used conan with its "PkgConfigDeps"-generator to generate ".pc"-files and fed these files to the qbspkgconfig module provider. In the generated modules the "cpp.dynamicLibraries" contained the libraries in the wrong order, e.g. '"fmt", "spdlog"' but spdlog should be linked before fmt.

Setting "mergeDependencies" to "false" leads to the right library order.