MSVC and Itanium mangling use different mangling numbers
for function-scope structs, which causes inconsistent
mangled kernel names in device and host compilations.
This patch uses Itanium mangling number for structs
in for mangling device side names in CUDA/HIP host
compilation on Windows to fix this issue.
A state is added to ASTContext to indicate whether the
current name mangling is for device side names in host
compilation. Device and host mangling number
are encoded/decoded as upper and lower half of 32 bit
unsigned integer to fit into the original mangling number
field for AST. Diagnostic will be emitted if a manglining
number exceeds limit.
Reviewed by: Artem Belevich, Reid Kleckner
Differential Revision: https://reviews.llvm.org/D122734
Fixes: SWDEV-328515
