MSVC: disable frequent compiler warnings
Using uninitialized variables to initialize themselves (i.e. 'type varname
= varname;') seems to be a frequent pattern in git. This is supposedly to
suppress the 'using uninitialized variable' warning, which is a bit
paradox, but seems to work with most compilers. MSVC correctly complains
here - disable C4090 warning.
MSVC also warns about implicit casts from non-const to const, which is
stupid - disable C4700 warning.
MSVC link.exe doesn't recognize the /wd option in CFLAGS in the Makefile,
so use #pragma warning in central, MSVC-specific unistd.h.
Signed-off-by: Karsten Blees <blees@dcon.de>