git-compat-util.h: do not #include <sys/param.h> by default

Earlier we allowed platforms that lack <sys/param.h> not to include
the header file from git-compat-util.h; we have included this header
file since the early days back when we used MAXPATHLEN (which we no
longer use) and also depended on it slurping ULONG_MAX (which we get
by including stdint.h or inttypes.h these days).

It turns out that we can compile our modern codebase just file
without including it on many platforms (so far, Fedora, Debian,
Ubuntu, MinGW, Mac OS X, Cygwin, HP-Nonstop, QNX and z/OS are
reported to be OK).

Let's stop including it by default, and on platforms that need it to
be included, leave "make NEEDS_SYS_PARAM_H=YesPlease" as an escape
hatch and ask them to report to us, so that we can find out about
the real dependency and fix it in a more platform agnostic way.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -104,7 +104,7 @@
 #endif
 #include <errno.h>
 #include <limits.h>
-#ifndef NO_SYS_PARAM_H
+#ifdef NEEDS_SYS_PARAM_H
 #include <sys/param.h>
 #endif
 #include <sys/types.h>