depends: set LANG=C in Makefile

[fanquake]

While testing some of @theuni's work for iOS cross builds in depends, I found a locale related issue that appears when preprocessing OpenSSL's Configure. This is on macOS 10.13.5.

7ac0c67 (a subset of the iOS related build changes) is included to show the issue.
When doing a depends build with master (6579d80) + that commit I see:

cd depends
make -j5
<snip>
Extracting openssl...
bitcoin/depends/sources/openssl-1.0.1k.tar.gz: OK
Preprocessing openssl...
sed: RE error: illegal byte sequence
make: *** [bitcoin/depends/work/build/x86_64-apple-darwin17.6.0/openssl/1.0.1k-b6eae8817ad/.stamp_preprocessed] Error 1

It seems like the issue could be related to embedded double quotes.

I did try setting other locale related variables:
LANGUAGE=C
LC_ALL=C
LC_CTYPE=C
etc, however LANG=C was the only one that actually seemed to work.

This is the output of locale on my machine:

$ locale
LANG="en_AU.UTF-8"
LC_COLLATE="en_AU.UTF-8"
LC_CTYPE="en_AU.UTF-8"
LC_MESSAGES="en_AU.UTF-8"
LC_MONETARY="en_AU.UTF-8"
LC_NUMERIC="en_AU.UTF-8"
LC_TIME="en_AU.UTF-8"
LC_ALL=

Todo:

• Confirm this isn't a local issue.
• Should we also set other locale related vars?
• Followup other uses of sed in /depends/packages.

[practicalswift]

Weird! Shouldn't LANG be used only in the absence of other locale related environment variables?

locale(1) from OS X:

     LANG         Used as a substitute for any unset LC_* variable.  If LANG is unset, 
                  it will act as if set to "C".  If any of LANG or LC_* are set to invalid
                  values, locale acts as if they are all unset.

     LC_ALL       Will override the setting of all other LC_* variables.

locale(7) from Linux:

       If the second argument to setlocale(3) is an empty string, "", for the default
       locale, it is determined using the following steps:

       1. If there is a non-null environment variable LC_ALL, the value of LC_ALL is used.

       2. If an environment variable with the same name as one of the categories
          above exists and is non-null, its value is used for that category.

       3. If there is a non-null environment variable LANG, the value of LANG is used.

[DrahtBot]

The last travis run for this pull request was 50 days ago and is thus outdated. To trigger a fresh travis build, this pull request should be closed and re-opened.

[DrahtBot]

Reviewers, this pull request conflicts with the following ones:

• [WIP] 64 bit iOS device support  #12557 ([WIP] 64 bit iOs device support by Sjors)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[fanquake]

Going to close this for now. It can be worked around in other ways.