Unable to compile 0.15 on Cygwin (strerror_r was not declared) #12049

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Issue Description: Unable to compile and build bitcoin 0.15

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Expected behavior: Successful build :)

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Actual Behavior: Build breaks -> https://pastebin.com/GYZtKBNC Update #1: https://pastebin.com/9Svrbn8g

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Triage/Reproduce the issue: https://pastebin.com/UcWnt8dc

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Version of bittcoin core: 0.15 (downloaded from github)

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Type of machine on which issue occured: $ uname -a CYGWIN_NT-6.1-WOW pluto 2.9.0(0.318/5/3) 2017-09-12 10:41 i686 Cygwin

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<!--- This is normally the contents of a `debug.log` or `config.log` file. Raw text or a link to a pastebin type site are preferred. -->

Extra information/updates SO question I have created on this -> https://stackoverflow.com/questions/48008080/c-compilation-stuck-with-boost-interprocess-lib-error-ftruncate-has-not/48008425?noredirect=1#comment83027051_48008425

Latest config.log -> https://pastebin.com/1q4hzeqD Latest error console output -> https://pastebin.com/9Svrbn8g

As far as I know, no one is building this on cygwin. You're free to try, but if you want to build for windows, you'll save yourself a lot of pain by following the windows build instructions in https://github.com/bitcoin/bitcoin/blob/master/doc/build-windows.md.

I dont have Windows 10 and I did try MinGW.... with no success at all. The only shot I have of some success is with cygwin and I believe I did make some progress... Will update OP with this. I am currently stuck with

netbase.cpp:720:41: error: `strerror_r' was not declared in this scope
     if (strerror_r(err, buf, sizeof(buf)))

which might be caused because of no glibc support (perhaps) in cygwin, so maybe I have to try something like newlib ? Not really sure... some help/advice would be great !

I have pastebin'ed the latest config.log link and the error console output in the OP....

@ZeroGraviti On which OS are you trying to do this?

@ZeroGraviti You can compile on any OS, the main thing is to work on a virtualbox https://github.com/bitcoin/bitcoin/blob/0.15/doc/gitian-building.md

@DATSEC @molxyz @laanwj The compilation is because <string.h> is probably not being included somewhere somehow. The function strerror_r() is not being declared in the scope in which it is used in netbase.cpp. So, it's not being included somewhere, or perhaps it just isn't there within Cygwin. However, I believe it's under the newlib source files in Cygwin which implement the strerror_r() function.

Is this still an issue with a recent version of Bitcoin Core? If yes, what are the steps to reproduce?