Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Provide slightly more helpful feedback when we can't figure out what
compiler the user is using.

PR: misc/173914

Fix typo in bsd.compiler.mk.

Allow CC to be gcc46 or similar by matching gcc*.

Don't test the value of the :M matches, either the string matches or does
not.

Add a COMPILER_FEATURES variable that is set in bsd.compiler.mk.

When the compiler is clang add c++11 to COMPILER_FEATURES.

When the compiler supports c++11, default to building libc++. This will
not impact the compliation of programs, but will make it easier for
users with clang compiled systems to test libc++ by passing -stdlib=libc++
to their c++ compliations.

Introduce a new make variable COMPILER_TYPE that specifies what
type of compiler is being used (currently clang or gcc). COMPILER_TYPE
is set in the new bsd.compiler.mk file based on the value of the CC
variable or, should it prove informative, by running ${CC} --version
and examining the output.

To avoid negative performance impacts in the default case and correct
value for COMPILER_TYPE type is determined and passed in the environment
of submake instances while building world.

Replace adhoc attempts at determining the compiler type by examining
CC or MK_CLANG_IS_CC with checks of COMPILER_TYPE. This eliminates
bootstrapping complications when first setting WITH_CLANG_IS_CC.

Sponsored by: DARPA, AFRL
Reviewed by: Yamaya Takashi <yamayan@kbh.biglobe.ne.jp>, imp, linimon
(with some modifications post review)
MFC after: 2 weeks