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/dtmailpr/Imakefile

@@ -40,10 +40,6 @@ MT_LIBS		=	-i $(C++_LIB)  -lm -lw -lc
 SYS_LIBRARIES	=	-lintl -lnsl $(MT_LIBS) -lC
 #endif /* SunArchitecture */
 
-#if defined(LinuxArchitecture)
-CXXEXTRA_DEFINES = -fpermissive
-#endif
- 
 SRCS = main.C message.C mailbox.C utils.C
 OBJS = main.o message.o mailbox.o utils.o