build,win: limit maxcpucount to 2 for MSBuild

MSBuild invokes cl.exe with /MP (set in common.gypi), making it
compile sources in parallel using a number of internal processes
equal to the number of effective processors. MSBuild /m uses a
similar mechanism, so the number of compiler processes can grow to
the number of effective processors squared.

This limits MSBuild to 2 processes, to still use some parallelization
while requiring less memory. Cl.exe is still invoked with /MP, thus
the maximum number of processes is limited to twice the number of
effective processors.

PR-URL: https://github.com/nodejs/node/pull/12184
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

vcbuild.bat

@@ -190,9 +190,11 @@ echo Project files generated.
 if defined nobuild goto sign
 
 @rem Build the sln with msbuild.
+set "msbcpu=/m:2"
+if "%NUMBER_OF_PROCESSORS%"=="1" set "msbcpu=/m:1"
 set "msbplatform=Win32"
 if "%target_arch%"=="x64" set "msbplatform=x64"
-msbuild node.sln /m /t:%target% /p:Configuration=%config% /p:Platform=%msbplatform% /clp:NoSummary;NoItemAndPropertyList;Verbosity=minimal /nologo
+msbuild node.sln %msbcpu% /t:%target% /p:Configuration=%config% /p:Platform=%msbplatform% /clp:NoSummary;NoItemAndPropertyList;Verbosity=minimal /nologo
 if errorlevel 1 goto exit
 if "%target%" == "Clean" goto exit