Where to add a CFLAG, such as -std=gnu99, into an (Eclipse CDT) autotools project
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I have a simple Autotools C project (not C++), whose skeleton was created for me by Eclipse CDT (Juno).

CFLAGs (by inspection) seem to be `-g -O2`.

I want all of the generated make files to also have `-std=gnu99` appended to the CFLAGs.

I can obviously hack the Makefile, but this gets overwritten on `./configure`.

Where is the correct place to add (or change) CFLAGs which are required by the code (as opposed to those CFLAGs which the user might want to change)?
