Add Cygwin to Appveyor

appveyor.yml

@@ -16,7 +16,6 @@ environment:
   matrix:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2013
       TOOLSET: msvc-9.0,msvc-10.0,msvc-11.0,msvc-12.0
-      ADDRMD: 32,64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       TOOLSET: msvc-14.0
       ADDRMD: 32,64
@@ -24,6 +23,14 @@ environment:
       TOOLSET: msvc-14.1
       CXXSTD: 14,17
       ADDRMD: 32,64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2013
+      ADDPATH: C:\cygwin\bin;
+      TOOLSET: gcc,clang
+      CXXSTD: 03,11,14,1z
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2013
+      ADDPATH: C:\cygwin64\bin;
+      TOOLSET: gcc,clang
+      CXXSTD: 03,11,14,1z
 
 install:
   - set BOOST_BRANCH=develop
@@ -53,6 +60,7 @@ install:
 build: off
 
 test_script:
+  - PATH=%ADDPATH%%PATH%
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
   - b2 -j3 libs/smart_ptr/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release