rustc_target: Inherit `windows_uwp_msvc_base` from `windows_msvc_base`
rustc_target: Inherit `windows_uwp_msvc_base` from `windows_msvc_base`

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust