windows build with non-english toolchain installation

[Ralf H]

Hallihallo,

when building on windows systems with non-english toolchains (in my
case, German), there are usually non-english COMPILER_VERSION_OUTPUTs to
be checked in make/autoconf/toolchain.m4.

Line 462 reads

    $ECHO "$COMPILER_VERSION_OUTPUT" | $GREP "Microsoft.*Compiler" >
/dev/null

but my german version reports as "Microsoft (R)
C/C++-Optimierungscompiler Version 19.15.26732.1 fr x64"

meaning the capital C in the GREP search should be either omitted or the
GREP made case-insensitive

Not sure if this covers *all* languages :)