We need to append-to rather than set CXXFLAGS, otherwise we loose -O2 &
-pipe. Currently this results in zeromq being built without optimizations
at all (or whatever the compiler would default too, essentially always -O0).
Bdb is the same, for the CXX portion of its code. C code has been built
with -O2.
Boost has actually been uneffected because it receives -O3 from it's own
build flags.
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