WINGs: Fix incorrect use of macro USE_PANGO in installed header
The header "WINGsP.h" needs different behaviour depending on whether the
support for Pango was enabled or not. But the related macro USE_PANGO is
defined by WindowMaker's configure, and after this header have been
installed the macro is no more valid.
This patch makes the "WINGsP.h" a generated file, so it will be different
depending on USE_PANGO, but will not make use of the macro itself.
As a side effect of being now generated, the include paths in the makefile
have been updated to include build-dir too, because for users doing an
out-of-tree build the generated file (that is used during compilation) is
placed in the build-dir.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>