Update variant to 91ba0301a672ea0a3131390d44d304c5493de84a, specifically this commit: https://github.com/mapbox/variant/commit/39a631394e185f527159164c8b0fffae755b8512, which fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68073 under GCC 5.2.1.

Fixes  #1758

third_party/variant/scripts/build-appveyor.bat

@@ -0,0 +1,32 @@
+@ECHO OFF
+SETLOCAL
+
+SET PATH=c:\python27;%PATH%
+
+ECHO activating VS command prompt
+IF /I "%PLATFORM"=="x64" (
+  CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64
+) ELSE (
+  CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86
+)
+
+IF NOT EXIST deps\gyp git clone --depth 1 https://chromium.googlesource.com/external/gyp.git deps/gyp
+
+CALL deps\gyp\gyp.bat variant.gyp --depth=. ^
+-f msvs ^
+-G msvs_version=2015 ^
+--generator-output=build
+
+SET MSBUILD_PLATFORM=%platform%
+IF /I "%MSBUILD_PLATFORM%" == "x86" SET MSBUILD_PLATFORM=Win32
+
+
+msbuild ^
+build\variant.sln ^
+/nologo ^
+/toolsversion:14.0 ^
+/p:PlatformToolset=v140 ^
+/p:Configuration=%configuration% ^
+/p:Platform=%MSBUILD_PLATFORM%
+
+build\"%configuration%"\tests.exe

third_party/variant/scripts/build-local.bat

@@ -0,0 +1,7 @@
+@ECHO OFF
+SETLOCAL
+
+SET platform=x64
+SET configuration=Release
+
+CALL scripts\build-appveyor.bat