Ordering them before the imports in the same file was not enough: a
project header on line 1 can import a module several levels down whose
global module fragment already pulled in the same standard header, and
that include guard does not cross the module boundary. Putting them
first means the guard is set before anything can import.
Skips vendored single-header libraries and anything inside an #if.
A header first pulled in through an imported module's global module
fragment leaves no include guard in the importing unit - macros do not
cross a module boundary - so a later textual include parses it again and
MSVC rejects the redefinition. Redoes the betterRenderer sweep with
placement that stays out of #if blocks, which is where the previous one
dropped <fstream> and broke nvrenderer_d3d12.cpp.
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.
