linux: build with thread safety and REENTRANT enabled.

There was a check in linux.cf for the Linux libc version that didn't
work, since these were never set anywhere.  Presumably current Xorg
imake sets these, but since we aren't using that... (yet)

As a result, the build assumed that thread-safe API's were not
supported.  Setting the default libc major version to '6' allows the
proper build to take place.  libc5 was never threadsafe and no one has
probably used it in over 10 years.

As a result, some earlier porting fixes that referenced '__fds_bits'
on linux systems had to be reverted as these are not valid in an MT
environment.  They are also not neccessary when building in such an
environment, as the normal 'fds_bits' works fine.

This patch defintely needs testing on many linux systems.

cde/config/cf/linux.cf

@@ -34,6 +34,17 @@ XCOMM platform:  $TOG: linux.cf /main/47 1998/04/17 11:32:51 mgreess $
     LinuxYggdrasil  (12)
 */
 #endif
+
+#ifndef DefaultLinuxCLibMajorVersion
+# define DefaultLinuxCLibMajorVersion    6
+#endif
+#ifndef DefaultLinuxCLibMinorVersion
+# define DefaultLinuxCLibMinorVersion    0
+#endif
+#ifndef DefaultLinuxCLibTeenyVersion
+# define DefaultLinuxCLibTeenyVersion    0
+#endif
+
 #ifndef LinuxCLibMajorVersion
 # define LinuxCLibMajorVersion           DefaultLinuxCLibMajorVersion
 #endif
@@ -43,6 +54,7 @@ XCOMM platform:  $TOG: linux.cf /main/47 1998/04/17 11:32:51 mgreess $
 #ifndef LinuxCLibTeenyVersion
 # define LinuxCLibTeenyVersion           DefaultLinuxCLibTeenyVersion
 #endif
+
 #ifndef LinuxBinUtilsMajorVersion
 # define LinuxBinUtilsMajorVersion	 DefaultLinuxBinUtilsMajorVersion
 #endif

cde/lib/csa/xtclient.c

@@ -69,11 +69,8 @@ _DtCm_register_xtcallback(XtAppContext appct)
 		return;
 
 	/* assuming only 1 bit is set */
-#if defined(linux)
-	bits = fdset.__fds_bits;
-#else
 	bits = fdset.fds_bits;
-#endif
+
 	for (i = 0; i < FD_SETSIZE; i += NFDBITS) {
 		fmask = *bits;
 		for (j = 0; fmask != 0; j++, fmask >>= 1) {

cde/programs/dtspcd/spcd_event.c

@@ -86,13 +86,8 @@ void SPCD_MainLoopUntil(Boolean *flag)
   int result;
   do {
     for (n=0; n<fd_vec_size; n++) {
-#if defined(linux)
-      input_mask.__fds_bits[n] = Sb_Input_Mask.__fds_bits[n];
-      except_mask.__fds_bits[n] = Sb_Except_Mask.__fds_bits[n];
-#else
       input_mask.fds_bits[n] = Sb_Input_Mask.fds_bits[n];
       except_mask.fds_bits[n] = Sb_Except_Mask.fds_bits[n];
-#endif
     }
     
     do result=select(SPCD_max_fd + 1, FD_SET_CAST(&input_mask),