Build issue: let user decide the MASTER_PROJECT variable

[randomizedthinking]

This is a small question on building the fmt library. In my use case, fmt is included as a git submodule, and I would like to build and install fmt automatically along with the main project. Yet, the current fmt CMakefile would not allow me to do it because the MASTER_PROJECT variable in CMakeLists.txt is determined in the build time.

The solution would be straightforward: define a FMT_MASTER_PROJECT and check whether it is defined before setting it up. If you think it is worthwhile to have, I can submit a PR.

if(NOT DEFINED FMT_MASTER_PROJECT)
    if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
        set(FMT_MASTER_PROJECT ON)
    else()
        set(FMT_MASTER_PROJECT OFF)
    endif()
endif()

[vitaut]

Sounds reasonable. Please submit a PR to make MASTER_PROJECT configurable.