The Makefile function `version_is_greater_or_equal` is used to check if
a version of GNU Make is at least the required one. However, it has
the built-in assumption the version numbers have to format x.y.z,
but Alpine Linux currently ships GNU Make 4.4. This results in
`$(call _pad_number,3,)` which runs `printf '$03d' ''` in the shell,
which is not valid.
This fixes the issue by making `_pad_number` more robust by fall back to
printing `0` with the given padding, if the number given to print is
empty.
Add make only function to convert strings to lowercase and uppercase.
This can replace the `$(shell echo $(var) | tr 'a-z-' 'A-Z_')` pattern.
Using the 'make' implementation results in being around 100 times faster.