Import EXTERNAL_INCLUDE env variable from VS dev environment (#4817)

* Initial plan

* Add EXTERNAL_INCLUDE to VS dev environment variables (#4217)

The EXTERNAL_INCLUDE environment variable set by vcvarsall.bat was not
being captured, causing MSVC's external-header diagnostic suppression
to not work when building through CMake Tools.

Co-authored-by: Omotola <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: Omotola <[email protected]>
Co-authored-by: Omotola <[email protected]>

Author: Copilot

CHANGELOG.md

@@ -31,6 +31,7 @@ Improvements:
 - Honor `debugger.workingDirectory` from the CMake File API when debugging a target, so that the `DEBUGGER_WORKING_DIRECTORY` target property is used as the debugger working directory. [#4595](https://github.com/microsoft/vscode-cmake-tools/issues/4595)
 
 Bug Fixes:
+- Import the `EXTERNAL_INCLUDE` environment variable from the VS developer environment so that MSVC's external-header diagnostic suppression works correctly. [#4217](https://github.com/microsoft/vscode-cmake-tools/issues/4217)
 - Fix test presets not automatically switching when the build preset changes in multi-config generator setups (e.g., Ninja Multi-Config). The extension now auto-selects a compatible test preset after a build preset change, and properly considers build type when guessing the test preset. [#4395](https://github.com/microsoft/vscode-cmake-tools/issues/4395)
 - Fix `cmake.additionalCompilerSearchDirs` ignoring per-folder overrides in multiroot workspaces. The setting is now read from each folder's scoped configuration with `${workspaceFolder}` expanded per-folder, and the results are unioned. Also fix `cmake.cmakePath` resolution during kit scanning to try all workspace folders instead of only the first.
 - Fix `${workspaceFolder}` expansion in `cmake.additionalCompilerSearchDirs` for single-root workspaces. Previously only the multi-root `${workspaceFolder:name}` syntax worked. [#4571](https://github.com/microsoft/vscode-cmake-tools/issues/4571)

src/installs/visualStudio.ts

@@ -258,6 +258,7 @@ const msvcEnvVars = [
     'FrameworkVersion',
     'FrameworkVersion32',
     'FrameworkVersion64',
+    'EXTERNAL_INCLUDE',
     'INCLUDE',
     'LIB',
     'LIBPATH',