configure: support HAVE_BSD_SYSCTL option

On BSD-compatible systems some information such as the number
of available CPUs may only be available via the sysctl function.

Add support for a HAVE_BSD_SYSCTL option complete with autoconf
support and include the sys/syctl.h header when the option is
enabled to make the sysctl function available.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -348,6 +348,8 @@ all::
 #
 # Define NO_HMAC_CTX_CLEANUP if your OpenSSL is version 0.9.6b or earlier to
 # cleanup the HMAC context with the older HMAC_cleanup function.
+#
+# Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1414,6 +1416,10 @@ ifdef HAVE_CLOCK_MONOTONIC
 	BASIC_CFLAGS += -DHAVE_CLOCK_MONOTONIC
 endif
 
+ifdef HAVE_BSD_SYSCTL
+	BASIC_CFLAGS += -DHAVE_BSD_SYSCTL
+endif
+
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK = NoThanks
 endif

config.mak.uname

@@ -107,6 +107,7 @@ ifeq ($(uname_S),Darwin)
 	COMPAT_OBJS += compat/precompose_utf8.o
 	BASIC_CFLAGS += -DPRECOMPOSE_UNICODE
 	BASIC_CFLAGS += -DPROTECT_HFS_DEFAULT=1
+	HAVE_BSD_SYSCTL = YesPlease
 endif
 ifeq ($(uname_S),SunOS)
 	NEEDS_SOCKET = YesPlease
@@ -199,6 +200,7 @@ ifeq ($(uname_S),FreeBSD)
 	PYTHON_PATH = /usr/local/bin/python
 	HAVE_PATHS_H = YesPlease
 	GMTIME_UNRELIABLE_ERRORS = UnfortunatelyYes
+	HAVE_BSD_SYSCTL = YesPlease
 endif
 ifeq ($(uname_S),OpenBSD)
 	NO_STRCASESTR = YesPlease
@@ -208,6 +210,7 @@ ifeq ($(uname_S),OpenBSD)
 	BASIC_CFLAGS += -I/usr/local/include
 	BASIC_LDFLAGS += -L/usr/local/lib
 	HAVE_PATHS_H = YesPlease
+	HAVE_BSD_SYSCTL = YesPlease
 endif
 ifeq ($(uname_S),MirBSD)
 	NO_STRCASESTR = YesPlease
@@ -215,6 +218,7 @@ ifeq ($(uname_S),MirBSD)
 	USE_ST_TIMESPEC = YesPlease
 	NEEDS_LIBICONV = YesPlease
 	HAVE_PATHS_H = YesPlease
+	HAVE_BSD_SYSCTL = YesPlease
 endif
 ifeq ($(uname_S),NetBSD)
 	ifeq ($(shell expr "$(uname_R)" : '[01]\.'),2)
@@ -225,6 +229,7 @@ ifeq ($(uname_S),NetBSD)
 	USE_ST_TIMESPEC = YesPlease
 	NO_MKSTEMPS = YesPlease
 	HAVE_PATHS_H = YesPlease
+	HAVE_BSD_SYSCTL = YesPlease
 endif
 ifeq ($(uname_S),AIX)
 	DEFAULT_PAGER = more

configure.ac

@@ -1046,6 +1046,29 @@ GIT_CONF_SUBST([NO_INITGROUPS])
 #
 # Define NO_ICONV if your libc does not properly support iconv.
 
+AC_DEFUN([BSD_SYSCTL_SRC], [
+AC_LANG_PROGRAM([[
+#include <stddef.h>
+#include <sys/types.h>
+#include <sys/sysctl.h>
+]],[[
+int val, mib[2];
+size_t len;
+mib[0] = CTL_HW;
+mib[1] = 1;
+len = sizeof(val);
+return sysctl(mib, 2, &val, &len, NULL, 0) ? 1 : 0;
+]])])
+
+#
+# Define HAVE_BSD_SYSCTL=YesPlease if a BSD-compatible sysctl function is available.
+AC_MSG_CHECKING([for BSD sysctl])
+AC_COMPILE_IFELSE([BSD_SYSCTL_SRC],
+	[AC_MSG_RESULT([yes])
+	HAVE_BSD_SYSCTL=YesPlease],
+	[AC_MSG_RESULT([no])
+	HAVE_BSD_SYSCTL=])
+GIT_CONF_SUBST([HAVE_BSD_SYSCTL])
 
 ## Other checks.
 # Define USE_PIC if you need the main git objects to be built with -fPIC

git-compat-util.h

@@ -127,6 +127,9 @@
 #else
 #include <poll.h>
 #endif
+#ifdef HAVE_BSD_SYSCTL
+#include <sys/sysctl.h>
+#endif
 
 #if defined(__MINGW32__)
 /* pull in Windows compatibility stuff */