travis: build V 4 times on Windows

.travis.yml

@@ -42,7 +42,13 @@ script:
       git clone --depth=1 https://github.com/ubawurinna/freetype-windows-binaries  thirdparty/freetype/
       echo "Just running ./make.bat to produce v.exe"
       ./make.bat
+      v.exe -o v2.exe compiler
+      v2.exe -o v3.exe compiler
+      v3.exe -o v4.exe compiler
       ls -la v.exe
+      ls -la v2.exe
+      ls -la v3.exe
+      ls -la v4.exe
       echo "Running v test v..."
       ./v.exe test v
       echo "Running v -os msvc test v..."