[v3] concept check macros, excess-errors

[Benjamin Kosnik]

> ...when the user configures with --enable-concept-checks, we still need a
> way to turn them off while building the library itself.  I have no problem
> with not doing this in the makefiles, but we should decide on how.

Why? I am aghast at the idea that the library won't build itself with 
concep checking turned on. This seems wrong.

> Or put a -D back in the makefile and change the test to
> 
>   #if !defined(_GLIBCPP_CONCEPT_CHECKS)
>       || defined (NO_WAY_IN_HELL_DO_WE_WANT_THESE_ON_RIGHT_NOW)
>   ...empty defines...
> 
> Or etc, etc.  Opinions solicited; choose yer poison.  :-)

Noooooooooooooooooooooooo.

I would think that if this is being done (not my first choice see above) 
it shoudl go here (say in src/Makefile.am)

CONFIG_CXXFLAGS = \
	@EXTRA_CXX_FLAGS@ @SECTION_FLAGS@ @CSHADOW_FLAGS@ @DEBUG_FLAGS@ 
	
-benjamin