Define ETIME for systems without that constant

ETIME alternative implementation as ETIMEDOUT is already available
for the work component, but not for the naemon component.

This fixes the following compilation error on systems without ETIME:

src/naemon/workers.c:517:27: error: use of undeclared identifier 'ETIME'
                if (wpres.error_code == ETIME) {
                                        ^
1 error generated.

src/naemon/workers.h

@@ -12,6 +12,10 @@
 
 #define WPROC_FORCE  (1 << 0)
 
+#ifndef ETIME
+#define ETIME ETIMEDOUT
+#endif
+
 NAGIOS_BEGIN_DECL
 
 typedef struct wproc_result {