CXXFeatures: update expected features and flags (Intel, SunPro)
CXXFeatures: update compiler matching in test

-use STREQUAL to compare the compiler ids, no need for regex here
-use CMAKE_CXX_COMPILER_ID to match g++ and MSVC
-match CMAKE_CXX_COMPILER_VERSION for MSVC instead of MSVC_VERSION, this is not
 only more consistent with the rest, it should also work if e.g. MSVC 10 uses
 MSVC 9 compiler
CXXFeatures: allow "better" compilers than expected

This can happen e.g. with old g++ with Clang plugin with more features, or
simply by a cstdint header in the system, maybe from another compiler.
CXXFeatures: add expected features for Clang

This is a bit vague as there seem to be some partial implementations in earlier
versions that are good enough to satisfy our tests.
CXXFeatures: compose full flag name only in check loop
Merge topic 'cxx11' into next

b8f006f CXXFeatures: compose full flag name only in check loop
0558337 CXXFeatures: add expected features for Clang
2f32ebc CXXFeatures: allow "better" compilers than expected
32384ed CXXFeatures: update compiler matching in test
61d407b CXXFeatures: update expected features and flags (Intel, SunPro)