compiler: bootstrap with MSVC

Add make_msvc.bat to bootstrap with msvc and test it with travis

.travis.yml

@@ -39,6 +39,8 @@ script:
   - |
     if [[ "${TRAVIS_OS_NAME}" == "windows" ]]; then
       choco install openssl.light
+      echo "Testing msvc bootstrapping"
+      ./make_msvc.bat
       echo "Running make_tests.bat..."
       ./make_tests.bat
     fi

make_msvc.bat

@@ -0,0 +1,48 @@
+@echo off
+
+set exiterror=0
+
+echo finding an MSVC installation
+
+for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do (
+  set InstallDir=%%i
+)
+
+REM set up a devcmd
+
+if exist "%InstallDir%\Common7\Tools\vsdevcmd.bat" (
+  call "%InstallDir%\Common7\Tools\vsdevcmd.bat" -arch=x64 -host_arch=x64
+) else (
+  goto :nomsvc
+)
+
+echo fetch v.c
+curl -O https://raw.githubusercontent.com/vlang/vc/master/v.c
+
+echo build v.c with msvc
+cl.exe /w /volatile:ms /D_UNICODE /DUNICODE /Fo.v.c.obj /O2 /MD v.c user32.lib kernel32.lib advapi32.lib shell32.lib /link /NOLOGO /OUT:v2.exe /INCREMENTAL:NO
+
+if %ERRORLEVEL% GEQ 1 (
+   goto :compileerror
+)
+
+echo rebuild from source
+v2.exe -o v.exe compiler
+
+del .v.c.obj
+del v.c
+del v2.exe
+
+exit
+
+:nomsvc
+echo Cannot find an msvc installation
+goto :error
+
+:compileerror
+echo Failed to compile - Create an issue at 'https://github.com/vlang' and tag '@emily33901'!
+goto :error
+
+:error
+echo Exiting from error
+exit /b 1

make_tests.bat

@@ -1,5 +1,10 @@
 @echo off
 
+echo Cleanup
+del v.exe
+del v.c
+del v2.exe
+
 echo fetch v.c
 curl -O https://raw.githubusercontent.com/vlang/vc/master/v.c
 if %ERRORLEVEL% NEQ 0 goto :fail
@@ -13,12 +18,16 @@ echo build v using vc
 vc.exe -o v.exe compiler
 if %ERRORLEVEL% NEQ 0 goto :fail
 
-echo build v.msvc using v
+echo build vc.msvc using vc
-v.exe -os msvc -o v.msvc.exe compiler
+vc.exe -os msvc -o v.msvc.exe compiler
 if %ERRORLEVEL% NEQ 0 goto :fail
 
-echo build v.msvc.2 using v.msvc
+echo build v.msvc.3 using v
-v.msvc.exe -os msvc -o v.msvc.2.exe compiler
+v.exe -os msvc -o v.msvc.2.exe compiler
+if %ERRORLEVEL% NEQ 0 goto :fail
+
+echo build v.msvc.3 using v.msvc
+v.msvc.exe -os msvc -o v.msvc.3.exe compiler
 if %ERRORLEVEL% NEQ 0 goto :fail
 
 echo build v.gcc using v.msvc