Removed conditional compilation from waitpid() error test.

There are reports that call to a signal handler for an exited process
despite waitpid() already called for the process may happen on Linux
as well.

src/os/unix/ngx_process.c

diff --git a/src/os/unix/ngx_process.c b/src/os/unix/ngx_process.c
index 5713ca8..4ef3582 100644
--- a/src/os/unix/ngx_process.c
+++ b/src/os/unix/ngx_process.c
@@ -474,8 +474,6 @@
                 return;
             }
 
-#if (NGX_SOLARIS || NGX_FREEBSD)
-
             /*
              * Solaris always calls the signal handler for each exited process
              * despite waitpid() may be already called for this process.
@@ -491,8 +489,6 @@
                 return;
             }
 
-#endif
-
             ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, err,
                           "waitpid() failed");
             return;