Build depends refer to source package names, not binary package names.

In many cases, PKG_BUILD_DEPENDS simply duplicated runtime dependencies of
a source package's binary packages; as the corresponding source packages
are implicitly added as bulid dependencies, PKG_BUILD_DEPENDS can simply be
dropped in these cases. In the other cases, *_BUILD_DEPENDS is fixed to
refer to the correct source package name.

Dependency of mysql-server is adjusted from libncursesw to libncurses
(as libncursesw is a virtual package provided by libncurses), so the build
dependency on ncurses is emitted unconditionally.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>