peas-dirs.c: Fix building on Visual Studio

libloadersapi.h should not have been included directly, just include
windows.h with WIN32_LEAN_AND_MEAN defined.
2 jobs for meson.msvc in 5 minutes and 24 seconds
Status Job ID Name Coverage
  Build
passed #932232
build peas

00:04:37

passed #932233
build peas-gtk

00:05:24