Do not restrict CMAKE_MODULE_PATH to a single path

[vaavaav]

Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)

More or less. It makes it harder to link bRPC against other projects.

Describe the solution you'd like (描述你期望的解决方法)

Instead of set(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake), allow the user to provide other paths while still maintaining this one:
set(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH}).
EDIT: list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")

With this, developers can provide other paths where Find<library>.cmake files exist, in the command line (for example, cmake -DCMAKE_MODULE_PATH=opt/lib/cmake.

Describe alternatives you've considered (描述你想到的折衷方案)

I had to manually copy Find<library>.cmake files to the path indicated by ${PROJECT_SOURCE_DIR}/cmake...

Additional context/screenshots (更多上下文/截图)

[chenBright]

Maybe it's better to use user specific paths first, like this: set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PROJECT_SOURCE_DIR}/cmake).

[vaavaav]

After searching a bit more, I stumble upon the suggestion of treating CMAKE_MODULE_PATH as a list of paths.
As such, list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake") is a much better practice.

[chenBright]

Good idea! Please check #2806.