The right way to use standard variable in configure.ac

[Andy Falanga (afalanga)]

Hi,

I placed the following in my configure.ac file:

CPPFLAGS="-DMACRO1 -DMACRO2"

because I found that as an example on a webpage someplace.  I reviewed so many 
learning about the autotools that I don't recall which one now.  I did this 
because there were some preprocessor flags that I wanted to have common to all 
sub-makefiles.

I ran into a problem today, however, where I needed to add a -I directive to my 
CPPFLAGS in order to find the necessary headers.  Then, the problem stepped in. 
 Because I placed this line in configure.ac, it was transcribed, verbatim (as 
it should), into configure.  The net result: not matter what I placed on the 
command line was ignored.  For example, the following:

CPPFLAGS=-I/path/to/the/alternate/location ./configure --build=x86_64-linux 
--host=arm-poky-linux-gnueabi

The additional path wasn't being appended, it was being stomped.  Did I miss a 
macro?  How should this be done because, obviously, I've gotten it incorrect.

Thanks,
Andy