inlined g_str_has optimisations

Submitted by Ben @bdejean

Link to original bug (#151957)

Description

gcc is able to emit optimized code for (str|strn|mem)cmp( str, "literal" ). The current g_str_has_prefix / g_str_has_suffix does not allow this. I think using g_str_has_*( str, "literal" ) is a pretty common usage and worths this optimisation.

the following patch renames g_str_has_* to _g_str_has_* and defines 4 macros ( 2 to prevent multiple argument evaluation )

some benchmark results (debian gcc-3.4 -O2)

  for(i = 0; i < 100000000; ++i)
    {
      res += g_str_has_prefix(s, "Stargate");
      res += g_str_has_suffix(s, "Stargate");
      res += g_str_has_prefix(s, "Super");
      res += g_str_has_suffix(s, "docious");
    }

PPC G4 1GHZ orig 65s -> patched 22s XP 1,666GHZ orig 37s -> patched 16s

please, consider this patch.