From 8218aed118f3d84b011f8b87385704a8cd603d3d Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Tue, 15 Aug 2023 12:36:00 -0400
Subject: IntelLLVM: support marking include paths as SYSTEM directories

Also learn how to suppress warnings when possible.

See: https://discourse.cmake.org/t/icx-on-windows-supports-external-i/8739
---
 Help/release/dev/IntelLLVM-isystem-flag.rst | 6 ++++++
 Modules/Compiler/IntelLLVM.cmake            | 6 ++++++
 2 files changed, 12 insertions(+)
 create mode 100644 Help/release/dev/IntelLLVM-isystem-flag.rst

diff --git a/Help/release/dev/IntelLLVM-isystem-flag.rst b/Help/release/dev/IntelLLVM-isystem-flag.rst
new file mode 100644
index 0000000..bba3d26
--- /dev/null
+++ b/Help/release/dev/IntelLLVM-isystem-flag.rst
@@ -0,0 +1,6 @@
+IntelLLVM-isystem-flag
+----------------------
+
+* The :generator:`Ninja` and :generator:`NMake Makefiles` generators now use
+  the ``-external:I`` flag for system includes when using IntelLLVM as of
+  version 2021.4. The ``-external:W0`` flag is also used as of version 2022.2.
diff --git a/Modules/Compiler/IntelLLVM.cmake b/Modules/Compiler/IntelLLVM.cmake
index f3c0bf4..a58128a 100644
--- a/Modules/Compiler/IntelLLVM.cmake
+++ b/Modules/Compiler/IntelLLVM.cmake
@@ -36,6 +36,12 @@ if(CMAKE_HOST_WIN32)
     __compiler_intel_llvm_common(${lang})
     set(CMAKE_${lang}_COMPILE_OPTIONS_IPO "-Qipo")
     set(CMAKE_${lang}_LINK_OPTIONS_IPO "-Qipo")
+    if (CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2021.4")
+      set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-external:I")
+      if (CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2022.2")
+        set(_CMAKE_INCLUDE_SYSTEM_FLAG_${lang}_WARNING "-external:W0 ")
+      endif ()
+    endif ()
   endmacro()
 else()
   # GNU-like
-- 
cgit v0.12