Nested func attr and gcc < 4.5

[Vladimir 'φ-coder/phcoder' Serbinenko]

Hello, all. It seems that NESTED_FUNC_ATTR strikes again. This time 
since most of our devs use  gcc >= 4.5 (I use 4.6) where the compiler 
bug is fixe, it's a bigger problem than before. So I propose the 
following: If gcc has this bug, compile with mregparms=1 and show a 
message recommendation to upgrade. Since we may be unable to execute 
target programs, we have to rely on version check but it shouldn't cause 
much trouble. This way we continue to support gcc < 4.5 without 
sacrificing reliability and finally get rid of the need of 
NESTED_FUNC_ATTR. The only downside is increased binary size with gcc < 4.5.

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Regards
Vladimir 'φ-coder/phcoder' Serbinenko