[gobject-introspection/clang-cl] MSVC.README.rst: Mention about the clang-cl support

[Chun-wei Fan <fanchunwei src gnome org>]

commit ef428e88dc04bfedb40f0ccd61b01da7ca139aa2
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Tue Aug 25 15:40:52 2020 +0800

    MSVC.README.rst: Mention about the clang-cl support
    
    Let people know how building G-I and running g-ir-scanner with clang-cl and
    friends is being supported, as this support is now added.

 MSVC.README.rst | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/MSVC.README.rst b/MSVC.README.rst
index d8941de43..ec5ddb566 100644
--- a/MSVC.README.rst
+++ b/MSVC.README.rst
@@ -109,3 +109,12 @@ the following so that we ensure the manifests are embedded to the built DLLs and
 
   for /r %f in (*.dll.manifest) do if exist $(PREFIX)\bin\%~nf mt /manifest %f 
/outputresource:$(PREFIX)\bin\%~nf;2
   for /r %f in (*.exe.manifest) do if exist $(PREFIX)\bin\%~nf mt /manifest %f 
/outputresource:$(PREFIX)\bin\%~nf;1
+
+Additional notes on using clang-cl (LLVM/CLang's Visual Studio compiler emulation)
+----------------------------------------------------------------------------------
+Support has been added to build GObject-Introspection with clang-cl, specifically for
+running g-ir-scanner with clang-cl and lld-link as the compiler and linker.  To enable
+such support, you need to set *both* the environment variables CC and CXX to clang-cl
+prior to building GObject-Introspection or running g-ir-scanner.  This is in line with
+building with clang-cl in place of using the stock Visual Studio compiler to perform
+builds with the Meson build system.