Make sysctl name2oid shared-locked as well.

This is a follow-up to r273401.
The dependencies are computed with CC even if sources are C++, when building
when building with an external gcc, we want to be able to pass the path to
the libc++ headers so dependencies are correctly computed for C++ source files.
Add a DEPFLAGS for that purpose

Reviewed by:	imp
When using an external toolchain note that gcc 4.8+ supports C++11

Submitted by:	imp
Always use libc++ as the default c++ stack when building with an external gcc 4.8+
While here disable building gcc from base when using gcc 4.8+

Reviewed by:	imp
When using an external gcc 4.8+ and not building libstdc++ then create in the objectdir a
fake libstdc++.so and libstdc++.a which is a symlink on libc++ that allow g++ to satisfy
its links dependencies in the least hackish way.
Please note that this hacky libstds++ never get installed on the final system

Reviewed by:	imp
Make the external toolchain support grows to the knowleged of XXFLAGS for C++ dedicated flags
and DEPFLAGS for mkdep flags
Pass the path to the libc++ headers in both, enforce the gnu++11 standard in the XXFLAGS
to satisfy libc++ requirements pass the libc++ objectdir as a location where to find
libraries so it can find libstdc++.so and libstdc++.A

Reviewed by:	imp
Do not make ld(1) warnings fatal anymore, binutils behaviour has changed over the
time and gnu.warnings.symbol are now being fatal preventing building world.

in the futur we want to investigate only making the gnu.warning.symbol non fatal

Reviewed by:	imp
Add sys/socket.h #include for bind(2), et al

Sponsored by: EMC / Isilon Storage Division