On Windows, read-only files cannot be deleted. To make sure that
deletion does not fail because of this, always call chmod() before
unlink().
Signed-off-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>

The wrapper does two things:
- Requests to open /dev/null are redirected to open the nul pseudo file.
- A request to open a file that currently exists as a directory on
  Windows fails with EACCES; this is changed to EISDIR.
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>

GIT's guts work with a forward slash as a path separators. We do not change
that. Rather we make sure that only "normalized" paths enter the depths
of the machinery.

We have to translate backslashes to forward slashes in the prefix and in
command line arguments. Fortunately, all of them are passed through
functions in setup.c.

A macro has_dos_drive_path() is defined that checks whether a path begins
with a drive letter+colon combination. This predicate is always false on
Unix. Another macro is_dir_sep() abstracts that a backslash is also a
directory separator on Windows.
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>

Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>

With this change GIT can be compiled and linked using MinGW. Builtins
that only read the repository such as the log family and grep already
work.

Simple stubs are provided for a number of functions that the Windows C
runtime does not offer. They will be completed in later patches.
However, a fix for the snprintf/vsnprintf replacement is applied here
to avoid buffer overflows.

Dmitry Kakurin pointed out that access(..., X_OK) would always fails on
Vista and suggested the -D__USE_MINGW_ACCESS workaround.
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>