Allow cli option to specify a directory for the build other than build/

[connoraird]

Description

Currently fpm enforces the naming of the output build director to be build. It would be useful to be able specify a different directory for this build dir, such as the -B and --build flags in cmake.

This would be useful if multiple compilers are being tested, to name one example.

Possible Solution

No response

Additional Information

No response

[perazz]

Cases were made against relaxing the directory structure constraitns. However, one option wout be to mimic Cargo:

Temporary (per build):

FPM_BUILD_DIR=custom_build_folder fpm build

Manifest:

[build]
target-dir = "custom_build_folder"