ASM_MASM: Populate MSVC runtime library abstraction table
In commit fb3370b6a1 (MSVC: Add abstraction for runtime library
selection, 2019-04-10, v3.15.0-rc1~229^2) we overlooked populating the
runtime library selection flags for the Microsoft assembler. It does
not actually have any such flags, but since its compiler id is `MSVC`
our generators expect the table to be populated. Use empty values.
Without this fix, enabling the `ASM_MASM` language with policy `CMP0091`
set to `NEW` causes an error due to the missing table entries.
Fixes: #20236, #19453