clang's GNU driver read /DELAYLOAD:dxcompiler.dll as a file name. CMake's
LINKER: prefix emits -Xlinker for it and passes it bare under MSVC.
The other raw linker flags in the tree sit inside if(MSVC), which is
false for this driver, so they never reach the command line.
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.
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.
MS DXC on Windows (at least IDxcUtils::BuildArguments) does not support forward slashes in UNC paths. This change feeds it native format with backslashes.
This makes it possible to build Linux and Windows binaries from a single source on a network share.
