0be03c7 Qt: Use _putenv_s instead of setenv on Windows builds (Brian McMichael)
Pull request description:
Fixes https://github.com/bitcoin/bitcoin/issues/10836
Error message I would get on `make`:
```
...
CXXLD bench/bench_bitcoin.exe
OBJCXXLD qt/bitcoin-qt.exe
qt/test/test_main.cpp: In function ‘int main(int, char**)’:
qt/test/test_main.cpp:64:43: error: ‘setenv’ was not declared in this scope
setenv("QT_QPA_PLATFORM", "minimal", 0);
^
make[2]: *** [qt/test/qt_test_test_bitcoin_qt-test_main.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory `/home/bmcmichael/Projects/bcoin/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/bmcmichael/Projects/bcoin/src'
make: *** [all-recursive] Error 1
```
`setenv` function is not available from the Microsoft runtime library. Need to use `_putenv_s` instead.
This solution tells the compiler to use `_putenv_s` on `WIN32` compilation (Note: this also works on 64-bit Windows instances.) and `setenv` everywhere else.
I've tested builds on Windows 10 x64 and Ubuntu 16.04 with this code.
---
Backport of Core PR10899