Once more, C++11 and older 'base' compilers

[coypu%sdf.org@localhost]

Hi,

I'm proposing this option:
per OS/arch combos _TARGET_HAS_PKGSRC_GCC.


if _TARGET_HAS_PKGSRC_GCC.
USE_LANGUAGE=c++   =>   GCC_REQD+=4.8

We will bump this if packages with more than 500-1000 dependencies
requires more. No going back to pre-4.8 for C++.


else
USE_LANGUAGE=c++11 =>  GCC_REQD+=4.8
(??? C++14, C++17, C++2a)

if CC_VERSION < GCC_REQD
=> PKG_FAIL_REASON="Not in _TARGET_HAS_PKGSRC_GCC, yadda yadda to
   override, possibly build from a system compiler"



Also for both, possibly provide a bootstrap warning about GCC<4.8.

currently I can say for netbsd/x86 we can safely add
_TARGET_HAS_PKGSRC_GCC, presumably sunos and linux too.