qmake ignores precompiled headers in C projects on mswindows/vc++

In the generated Makefiles, compilation rules for C files do not contain any references to precompiled headers. Neither is there a rule generating a C style precompiled header (using -TC instead of -TP).

On Linux, precompiled headers for C files are handled correctly by including dependencies to both versions of a precompiled header and rules to create both versions in two different files.