A template defined in a module interface is instantiated in the importing
unit, where its body's types must be complete. A declaration reaching the
importer only through the interface's global module fragment is not
enough for MSVC: cParser::operator>> uses std::stringstream, and every
unit that parsed a float got an incomplete type.
526 headers across 161 units, derived from what each interface's template
bodies actually name.
Its sources reached the standard library through the project headers they
included; those are imports now. 178 headers across 56 files, plus 18 C
library headers elsewhere for memcpy/printf and friends. MSVC's STL does
not supply these transitively the way libstdc++ does.
