Enabled tests on Cygwin, enabled tests with GNU extensions on Cygwin and MinGW.

appveyor.yml

@@ -1,4 +1,5 @@
 # Copyright 2016, 2017 Peter Dimov
+# Copyright 2018 Andrey Semashev
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
@@ -32,12 +33,11 @@ environment:
     - TOOLSET: msvc-14.1
       ADDRESS_MODEL: 64
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
-# Boost.Thread does not compile for Cygwin
-#    - TOOLSET: gcc
-#      ADDRESS_MODEL: 64
-#      CXXSTD: 03,11
-#      ADDPATH: C:\cygwin64\bin
-#      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    - TOOLSET: gcc
+      ADDRESS_MODEL: 64
+      CXXSTD: 03,11,03-gnu,11-gnu
+      ADDPATH: C:\cygwin64\bin
+      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
     - TOOLSET: gcc
       ADDRESS_MODEL: 64
       CXXSTD: 03,11,14,03-gnu,11-gnu,14-gnu
@@ -67,15 +67,14 @@ environment:
     - TOOLSET: msvc-14.1
       ADDRESS_MODEL: 32
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
-# Boost.Thread does not compile for Cygwin
-#    - TOOLSET: gcc
-#      ADDRESS_MODEL: 32
-#      CXXSTD: 03,11
-#      ADDPATH: C:\cygwin\bin
-#      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
     - TOOLSET: gcc
       ADDRESS_MODEL: 32
-      CXXSTD: 03,11
+      CXXSTD: 03,11,03-gnu,11-gnu
+      ADDPATH: C:\cygwin\bin
+      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    - TOOLSET: gcc
+      ADDRESS_MODEL: 32
+      CXXSTD: 03,11,03-gnu,11-gnu
       ADDPATH: C:\mingw\bin
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
     - TOOLSET: gcc