osx: delay version computation on macOS builds
Before this patch, HGVER would be evaluated at the beginning of the make
execution, and would be unset because build/mercurial/ doesn't exist yet
at that point. Now we compute the version after the `make install` run
has completed.
This is backported to stable from
8626b44516c1, but that revision had an
error in the shell invocation syntax.
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..