Added ngx_ncpu detection for most *nix platforms.

This inaccurate detection by using sysconf(_SC_NPROCESSORS_ONLN) can improve
usage of the mutex lock optimization on multicore systems.

auto/unix

diff --git a/auto/unix b/auto/unix
index 398b9be..5ee8f37 100755
--- a/auto/unix
+++ b/auto/unix
@@ -721,3 +721,13 @@
 ngx_feature_libs=
 ngx_feature_test="struct dirent  dir; dir.d_type = DT_REG"
 . auto/feature
+
+
+ngx_feature="sysconf(_SC_NPROCESSORS_ONLN)"
+ngx_feature_name="NGX_HAVE_SC_NPROCESSORS_ONLN"
+ngx_feature_run=no
+ngx_feature_incs=
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="sysconf(_SC_NPROCESSORS_ONLN)"
+. auto/feature

src/os/unix/ngx_posix_init.c

diff --git a/src/os/unix/ngx_posix_init.c b/src/os/unix/ngx_posix_init.c
index 02642bd..eea65a9 100644
--- a/src/os/unix/ngx_posix_init.c
+++ b/src/os/unix/ngx_posix_init.c
@@ -47,7 +47,13 @@
 
     for (n = ngx_pagesize; n >>= 1; ngx_pagesize_shift++) { /* void */ }
 
+#if (NGX_HAVE_SC_NPROCESSORS_ONLN)
     if (ngx_ncpu == 0) {
+        ngx_ncpu = sysconf(_SC_NPROCESSORS_ONLN);
+    }
+#endif
+
+    if (ngx_ncpu < 1) {
         ngx_ncpu = 1;
     }