debuginfo: Define int/float types in terms of MSVC-recognized types.

debuginfo:  Define int/float types in terms of MSVC-recognized types.

PDB debug information doesn't appear to be emitted for basic types.
By defining u32 as a typedef for unsigned __int32 when targeting MSVC,
we allow CDB and other debuggers to recognize "u32" as a type/expression.

This in turn unblocks rust-lang#70052 "Update hashbrown to 0.8.0" by
allowing $T1 ..= $T3 to resolve, which would otherwise fail to resolve
when builtin types fail to parse.