Provide a possibility to ignore duplicate symbols for exporting.

export.pas, texportlib:
  + new property "ignoreduplicates" with which duplicate symbols are ignored upon insertion
  + new method "duplicatesymbol" which checks "ignoreduplicates" and generates an error if it is False (this method needs to be used if a duplicate was detected)
expunix.pas, texportlibunix:
  * exportprocedure: use "duplicatesymbol" instead of always generating an error
systems/t_beos.pas, texportlibbeos:
  * exportprocedure: use "duplicatesymbol" instead of always generating an error
systems/t_haiku.pas, texportlibhaiku:
  * exportprocedure: use "duplicatesymbol" instead of always generating an error
systems/t_nwl.pas, texportlibnetwlibc:
  * exportprocedure: use "duplicatesymbol" instead of always generating an error
systems/t_nwm.pas, texportlibnetware:
  * exportprocedure: use "duplicatesymbol" instead of always generating an error
systems/t_win.pas, texportlibwin:
  * exportfromlist: use "duplicatesymbol" instead of always generating an error

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28792 3ad0048d-3df7-0310-abae-a5850022a9f2
psub.pas, read_proc:
  * don't generate assembler symbols for compiler internal code

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28793 3ad0048d-3df7-0310-abae-a5850022a9f2
Declare the indirect symbols as "Private for Extern".

ncgrtti.pas, TRTTIWriter:
  * write_rtti_extrasyms.enumdef_rtti_ord2stringindex, write_rtti_extrasyms.enumdef_rtti_string2ordindex & write_rtti: use AB_PRIVATE_EXTERN instead of AB_GLOBAL for the indirect symbol
ngenutil.pas, tnodeutils:
  * insertbssdata: use AB_PRIVATE_EXTERN instead of AB_GLOBAL for the indirect symbol
ptconst.pas, read_typed_const:
  * use AB_PRIVATE_EXTERN instead of AB_GLOBAL for the indirect symbol


git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28794 3ad0048d-3df7-0310-abae-a5850022a9f2
Correctly handle AB_PRIVATE_EXTERN in internal output writers.

ogbase.pas, TObjSymbol:
  * SetAddress: treat AB_PRIVATE_EXTERN like AB_GLOBAL

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28795 3ad0048d-3df7-0310-abae-a5850022a9f2