Add -fpermissive to linux standard c++ option define in linux.cf

Remove from individual Imakefiles.

Also, remove '#if 0' block in linux.cf, and remove empty
LinuxMachineDefines. This should be working correctly.  If not, let me
know.

cde/programs/dtmail/MotifApp/Imakefile

@@ -34,11 +34,6 @@ EXTRA_C++OPTIONS =     -xF +p +w $(SPRO_V3_OPTIONS)
 
 #endif /* SunArchitecture */
 
-#if defined(LinuxArchitecture)
-CXXEXTRA_DEFINES = -fpermissive
-#endif
-
-
 HEADERS = 
 
 SRCS = \