ncurses: Prevent LDFLAGS being emitted in .pc files

By default ncurses includes the values of LDFLAGS in its output
pkgconfig .pc files. This causes issues because OE includes options that
are specific to either the build host, or build configuration. These
options are not expected to be embedded in the pkgconfig output that is
installed.

Specifically this change resolves issues with uninative, where uninative
includes '-Wl,--dynamic-linker=' in LDFLAGS in order to force the
building and execution of native binaries against the dynamic linker
provided by uninative. This path is specific to TMPDIR at the time of
build, such that the installed files (and the associated sstate) have
this path. This prevents the sstate from being portable across build
directories/hosts.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>