Fix #14715 - detect tool fails on FreeBSD

[euantorano]

Fixes #14715

FreeBSD also requires linking the math library (see fenv). It seems NetBSD does too, though I haven't tested there.

Tested locally on FreeBSD and it appears to work - I now get a freebsd_amd64_consts.nim being generated at least.

[lbartoletti]

it still failed for me with nim 1.2.0 (from pkg) and devel. gcc not found

[euantorano]

Hi, that’s odd. I tested against a clean checkout with this patch applied and it worked there. It shouldn’t be trying to use gcc at all.

…

On Thu, 18 Jun 2020, at 19:42, lbartoletti wrote: it still failed for me with nim 1.2.0 (from pkg) and master. `gcc not found` — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#14716 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFW24LXYBY7ZUOPTYEDIGTRXJN2FANCNFSM4OBXANEQ>.

[euantorano]

CI failure seems unrelated.

I can't seem to replicate your problem @lbartoletti. Can you please explain the steps you took? My steps are as follows:

> git clone https://github.com/nim-lang/Nim.git
> cd Nim
> ./build_all.sh
> ./bin/nim c -r tools/detect/detect.nim

[lbartoletti]

@euantorano Yes, it's work. Sorry for the noise. I think there was a conflict with my installation. Dunno why I have to add a if at https://github.com/nim-lang/Nim/pull/14716/files#diff-d48a4f09dba4c4b83ca9f8cf908e2ca5R101