MIPS: reworked PIC/call code:
+ Favor 'weak' parameter in a_call_name of both thlcgmips and TCGMIPS.
* make_simple_ref and a_loadaddr_ref_reg: require input references to be 'raw' (no refaddr=addr_pic, etc) and do not use GP as base/index. If it's not true, raise an internal error. When addr_pic_call16 or so needs to be generated, it must be done without calling the mentioned methods.
* thlcgmips.a_call_name: generate PIC sequence for procedures declared as 'external', instead of 'cdecl', this is more correct because ABI has only one calling convention.
- make_simple_ref_fpu removed, there's no reason to handle references to floating-point data in different way.
- a_loadaddr_ref_cgpara override also removed, generic method does the job just well.
- thlcgmips.a_call_ref and a_call_reg overrides removed because indirect calls are now always done using $t9.


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23698 3ad0048d-3df7-0310-abae-a5850022a9f2