MFC r247527 (by brooks):

MFC r247527 (by brooks):
  Provide slightly more helpful feedback when we can't figure out what
  compiler the user is using.

  PR:		misc/173914

MFC r265829 (by imp):
  Support, to the extent we generate proper command lines, compiling
  with clang 3.3. Useful for test building -current on a -stable system
  in individual directories. Potentially useful if we ever want to
  support, say, gcc 4.8 or 4.9's new warnings when building with an
  external toolchain (but such support not yet committed). Document
  the bsd.compiler.mk interface.

MFC r266587 (by imp):
  Allow CC to not actually exist. During the ports INDEX run, all the
  Makefiles are evaluated without building things. In a normal build,
  the prerequisites would be built, and CC would be an actual thing. In
  an INDEX build, though, they don't exists. Redirect stderr to get rid
  of annoying messages, and assume that the compiler version is 0 if the
  actual compiler can't tell us. Do this in preference to guessing based
  on numbers because gcc410 might be 4.10, or 4.1.0 and without
  carefully crafted special knowledge we differentiate between them
  easily (also ming-gcc has no clues at all). Elsewhere, don't trust
  the compiler version if it is 0.

MFC r273405 (by bapt):
  When using an external toolchain note that gcc 4.8+ supports C++11

  Submitted by:	imp

MFC r275557 (by ngie):
  Fix typos in comments and wrap to <80 columns

MFC r275588 (by ngie):
  ${CC} --version doesn't need to be queried if both COMPILER_TYPE and
  COMPILER_VERSION are known

MFC r275589 (by ngie):
  The previous commit should have been a logical or not a logical "and"

  Pointyhat to: me

git-svn-id: svn://svn.freebsd.org/base/stable/9@279794 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f