Makefile.in: Change tm-svr4.h to tm-sysv4.h. Change xm-svr4.h

Makefile.in:  Change tm-svr4.h to tm-sysv4.h.  Change xm-svr4.h
to xm-sysv4.h.  Split OPCODE_DIR into OPCODE_DIR1 and OPCODE_DIR2
to reflect actual locations of opcode files, so TAGS target will
be buildable.

i386-tdep.c:  Change an erroneous 'm68k' reference to 'i386'.

i386-tdep.c (supply_fpregset, fill_fpregset):  Remove m68k code.

m68k-tdep.c (supply_fpregset, fill_fpregset):  Fix array
dereferencing to access the correct elements.

valops.c (value_addr):  Declare return type of external func value_copy().

xcoffread.c:  Undefine next_symbol_text before redefining it.