Add selection of std/nonstd version to batch scripts

[martinmoene]

Add selection of std/nonstd version to batch scripts.

See e.g. jthread-lite t.bat:

set std=c++14
if NOT "%1" == "" set std=%1 & shift

set select_jthread=jthread_CONFIG_SELECT_JTHREAD_NONSTD
if NOT "%1" == "" set select_jthread=%1 & shift

set args=%1 %2 %3 %4 %5 %6 %7 %8 %9

call :CompilerVersion version
echo VC%version%: %std% %select_jthread% %args%

set unit_config=^
    -Djthread_JTHREAD_HEADER=\"nonstd/jthread.hpp\" ^
    -Djthread_TEST_NODISCARD=1 ^
    -Djthread_CONFIG_SELECT_JTHREAD=%select_jthread%