V3 PATCH: numeric_limits<> support, fix PR/3865

[Graham Stott]

This patch causes problems building x86 cross v850-elf, and arm-elf toolchains
which both fail with

/usr/local/src/uberbaum/libstdc++-v3/src/limits.cc:56: error: excess elements
    in aggregate initializer
/usr/local/src/uberbaum/libstdc++-v3/src/limits.cc:58: error: excess elements
    in aggregate initializer
/usr/local/src/uberbaum/libstdc++-v3/src/limits.cc:60: error: excess elements
    in aggregate initializer
/usr/local/src/uberbaum/libstdc++-v3/src/limits.cc:62: error: excess elements
    in aggregate initializer

I suspect that other ports are also affected.

Graham