rewrite+improve asm parsing

- We now let the parser call the firm backend for constraint checking:
   - Error messages are displayed in parsing phase already and not delayed
     for ast2firm
   - We don't need to unconditionally set address_taken on all asm
   	 arguments
- Note: this also "fixes" testsuite/x86code/asm_test13.c. This is due to less
  unnecessary address taken being used, it does NOT fix the missing
  must-be-same handling in libfirm.
implement support for namend assembler operands
improve target triplet parsing with missing manufacturer

sparc-elf is accepted now.
update libfirm revision