workaround old version of /bin/date in msysgit

[tkelman]

I don't expect many people other than me to be trying to use msysgit as a build environment, but I found the version of /bin/date is pretty ancient there and running version_git.sh gives an error invalid date @1406586781'`.

Can someone test this on Mac, make sure using a switch case instead of an if statement doesn't break anything? Works okay on RHEL5, Ubuntu 14.04, Cygwin, MSYS2, and msysgit (wow I'm accumulating a crapton of different build environments).

I don't know the oldest version of git for which --pretty=format:%ci works, but that's pretty close to what we want here, so this could be cleaned up and unified across platforms instead of adding a special case for MSYS. TODO later?

[ivarne]

LGTM

# This file was autogenerated in base/version_git.sh
immutable GitVersionInfo
    commit::String
    commit_short::String
    branch::String
    build_number::Int
    date_string::String
    tagged_commit::Bool
    fork_master_distance::Int
    fork_master_timestamp::Float64
end

const GIT_VERSION_INFO = GitVersionInfo(
    "01fb9841abc91c3a31814a7f8871df6ad1468c20",
    "01fb984*",
    "tkelman/date-format",
    259,
    "2014-07-29 16:35 UTC",
    false,
    0,
    1406651706.
)

[ivarne]

--pretty=format:%ct is already in use for fork_master_timestamp. I did not use it last time to avoid breaking more than needed, but it seems like it can be done backwards compatible.

const GIT_VERSION_INFO = GitVersionInfo(
   #snip
    strftime("format_str", 1406651706),
   #snip
)

Maybe that should wait for the Dates module, so we can change the type as well.

[tkelman]

@vtjnash no hurry here, I think you owe everyone dinner #7774 (comment)

[vtjnash]

Haha, build fixes aren't new features

[tkelman]

Well, this is a build fix that affects me and so far only me, unless anybody else has given my MSVC PR a try.

[Keno]

LGTM. Works on Mac. Merging for now.

[tkelman]

Don't shoot me if it causes trouble on a BSD or something, but I don't think it should.