* xerces-c: Add variant for choice of transcoder (gnuiconv, iconv, icu,
macos, windows). It's important to specify a --enable-transcoder
option on the configure line or else xerces may make a different
choice when multiple transcoders are available.
* Pass the compile flags to configure. For cflags and cxxflags, this is
necessary to respect the value from the spack install line.
Otherwise, xerces (and any autotools package) will choose a default
value that overrides the spack compiler wrapper.
* Add xerces version 3.2.2.
* icu4c needs the --enable-rpath configure option on Darwin
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