Abusing XTRA_CXXFLAGS

[Rik]

10/30/13

All,

Someone may know why were doing this, otherwise I think it should change.

The build variable XTRA_CXXFLAGS is mostly used for machine-dependent
compiler flags necessary to guarantee IEEE numeric behavior.  However,
configure.ac is also adding in LLVM_CPPFLAGS, FreeType CPPFLAGS, etc. 
Since XTRA_CXXFLAGS are added to every C++ compile it means that really
low-level numeric stuff like liboctave/array/ is being compiled with '-I'
includes for FreeType.  It would seem better to move these very specific
flags out of the general compile command and use them only for the file or
Autotool sub-library that needs them.

Is this just evolutionary cruft left over from previous versions of
configure.ac, or is there a reason why we do this?

--Rik