Makefile.include: refactor command present check

[cladmi]

Contribution description

Refactor the code checking if command is present.
Message is taken from the compiler check as it was more precise than the others.

Testing

By overwriting the checked variables I correctly get the error

make -C examples/hello-world/ CC=hello-maintainer
make: Entering directory '/home/cladmi/git/work/RIOT/examples/hello-world'
Compiler hello-maintainer is required but not found in PATH.  Aborting.
make: *** [/home/cladmi/git/work/RIOT/examples/hello-world/../../Makefile.include:350: ..compiler-check] Error 1
make: Leaving directory '/home/cladmi/git/work/RIOT/examples/hello-world'

make -C examples/hello-world/ flash-only FLASHER=pleasemergeme
make: Entering directory '/home/cladmi/git/work/RIOT/examples/hello-world'
Flash program pleasemergeme is required but not found in PATH.  Aborting.
make: *** [/home/cladmi/git/work/RIOT/examples/hello-world/../../Makefile.include:409: flash] Error 1
make: Leaving directory '/home/cladmi/git/work/RIOT/examples/hello-world'

Issues/PRs references

Is part of #8838 PR

[aabadie]

Is it possible to move it in a separate .mk file in makefiles directory so it can be easily imported by other makefiles ? I think it could also be usefull for #8573.

[kaspar030]

Folo!

[aabadie]

Very useful PR. Thanks @cladmi

[kaspar030]

Nice one! And looong overdue! ;) ACK.