This is related to: microsoft/vscode-cmake-tools#2086

It looks like a non-mingw version of gcc is installed with MSYS2 by default, to c:\msys64\usr\bin. This version of gcc is similar to cygwin, in that it outputs unix-style include paths.

There is existing support for cygwin that remaps paths starting with /usr/lib/, but that fails to remap /usr/include when returned by this version of gcc. This issue is to track support for remapping all unix-style paths.