make relocation time symbol lookup and dlsym consistent

make relocation time symbol lookup and dlsym consistent

Using common code path for all symbol lookups fixes three dlsym issues:

- st_shndx of STT_TLS symbols were not checked and thus an undefined
  tls symbol reference could be incorrectly treated as a definition
  (the sysv hash lookup returns undefined symbols, gnu does not, so should
  be rare in practice).

- symbol binding was not checked so a hidden symbol may be returned
  (in principle STB_LOCAL symbols may appear in the dynamic symbol table
  for hidden symbols, but linkers most likely don't produce it).

- mips specific behaviour was not applied (ARCH_SYM_REJECT_UND) so
  undefined symbols may be returned on mips.

always_inline is used to avoid relocation performance regression, the
code generation for find_sym should not be affected.