docs: Document from_builtype mapping for b_vscrt [skip ci]
@@ -134,6 +134,19 @@ platforms or with all compilers:
The value of `b_sanitize` can be one of: `none`, `address`, `thread`,
`undefined`, `memory`, `address,undefined`.
+<a name="b_vscrt-from_buildtype"></a>
+The default value of `b_vscrt` is `from_buildtype`. In that case, the following
+table is used internally to pick the CRT compiler arguments based on the value
+of the `buildtype` option:
+
+| buildtype | Visual Studio CRT |
+| -------- | ----------------- |
+| debug | `/MDd` |
+| debugoptimized | `/MD` |
+| release | `/MD` |
+| minsize | `/MD` |
+| custom | error! |
+
### Notes about Apple Bitcode support
`b_bitcode` will pass `-fembed-bitcode` while compiling and will pass
