CASTOR-5123 RFE: Replace the C preprocessor variable linux with __linux__

Fixed.

mediachanger/castorrmc/common/Cnetdb.c

@@ -28,7 +28,7 @@ const char *name;
      *       provide thread safe version.
      */
     return(gethostbyname(name));
-#elif defined(linux)
+#elif defined(__linux__)
     static int hostent_key = -1;
     static int hostdata_key = -1;
     int rc;
@@ -69,7 +69,7 @@ int type;
      *       provide thread safe version.
      */
     return(gethostbyaddr(addr,len,type));
-#elif defined(linux)
+#elif defined(__linux__)
     static int hostent_key = -1;
     static int hostdata_key = -1;
     int rc;
@@ -109,7 +109,7 @@ const char *proto;
      *       provide thread safe version.
      */
     return(getservbyname(name,proto));
-#elif defined(linux)
+#elif defined(__linux__)
     static int servent_key = -1;
     static int servdata_key = -1;
     int rc;

mediachanger/castorrmc/common/serror.c

@@ -574,7 +574,7 @@ int sstrerror_r(const int n, char *const buf, const size_t buflen) {
      */
     tmpstr = sys_secerrlist[n-ESECBASEOFF];
   } else if ((n>0)
-#ifndef linux
+#ifndef __linux__
              && (n<sys_nerr)
 #endif
              ) {

mediachanger/castorrmc/common/strerror_r_wrapper.cpp

@@ -23,7 +23,7 @@
 
 #include "strerror_r_wrapper.h"
 
-#if defined(linux)
+#if defined(__linux__)
 /*
  * Undefine _GNU_SOURCE and define _XOPEN_SOURCE as being 600 so that the
  * XSI compliant version of strerror_r() will be used