tuklib_cpucores: Use cpuset_getaffinity() on FreeBSD if available.

In FreeBSD, cpuset_getaffinity() is the preferred way to get
the number of available cores.

Thanks to Rui Paulo for the patch. I edited it slightly, but
hopefully I didn't break anything.

m4/tuklib_cpucores.m4

@@ -45,6 +45,22 @@ compile error
 #endif
 ]])], [tuklib_cv_cpucores_method=special], [
 
+# FreeBSD has both cpuset and sysctl. Look for cpuset first because
+# it's a better approach.
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#include <sys/param.h>
+#include <sys/cpuset.h>
+
+int
+main(void)
+{
+	cpuset_t set;
+	cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID, -1,
+			sizeof(set), &set);
+	return 0;
+}
+]])], [tuklib_cv_cpucores_method=cpuset], [
+
 # Look for sysctl() solution first, because on OS/2, both sysconf()
 # and sysctl() pass the tests in this file, but only sysctl()
 # actually works.
@@ -97,9 +113,14 @@ main(void)
 ]])], [tuklib_cv_cpucores_method=pstat_getdynamic], [
 
 	tuklib_cv_cpucores_method=unknown
-])])])])])
+])])])])])])
 
 case $tuklib_cv_cpucores_method in
+	cpuset)
+		AC_DEFINE([TUKLIB_CPUCORES_CPUSET], [1],
+			[Define to 1 if the number of available CPU cores
+			can be detected with cpuset(2).])
+		;;
 	sysctl)
 		AC_DEFINE([TUKLIB_CPUCORES_SYSCTL], [1],
 			[Define to 1 if the number of available CPU cores

src/common/tuklib_cpucores.c

@@ -18,6 +18,11 @@
 #	endif
 #	include <windows.h>
 
+// FreeBSD
+#elif defined(TUKLIB_CPUCORES_CPUSET)
+#	include <sys/param.h>
+#	include <sys/cpuset.h>
+
 #elif defined(TUKLIB_CPUCORES_SYSCTL)
 #	ifdef HAVE_SYS_PARAM_H
 #		include <sys/param.h>
@@ -44,6 +49,19 @@ tuklib_cpucores(void)
 	GetSystemInfo(&sysinfo);
 	ret = sysinfo.dwNumberOfProcessors;
 
+#elif defined(TUKLIB_CPUCORES_CPUSET)
+	cpuset_t set;
+	if (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID, -1,
+			sizeof(set), &set) == 0) {
+#	ifdef CPU_COUNT
+		ret = CPU_COUNT(&set);
+#	else
+		for (unsigned i = 0; i < CPU_SETSIZE; ++i)
+			if (CPU_ISSET(i, &set))
+				++ret;
+#	endif
+	}
+
 #elif defined(TUKLIB_CPUCORES_SYSCTL)
 	int name[2] = { CTL_HW, HW_NCPU };
 	int cpus;