msvc: Fix build by adding missing symbol defines

In particular, remote-testsvn.c fails to compile with two
undeclared identifier errors relating to the 'UINT32_MAX'
and 'STDIN_FILENO' symbols.

In order to fix the compilation errors, we add appropriate
definitions for the UINT32_MAX and STDIN_FILENO constants
to an msvc compat header file.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Tested-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/vcbuild/include/unistd.h

@@ -49,6 +49,9 @@ typedef int64_t off64_t;
 #define INTMAX_MAX  _I64_MAX
 #define UINTMAX_MAX _UI64_MAX
 
+#define UINT32_MAX 0xffffffff  /* 4294967295U */
+
+#define STDIN_FILENO  0
 #define STDOUT_FILENO 1
 #define STDERR_FILENO 2