ncurses: enable-pc-files requires PKG_CONFIG_LIBDIR existed

ncurses: enable-pc-files requires PKG_CONFIG_LIBDIR existed

Fixed ncurses.do_configure:
configure: WARNING: did not find library /path/to/tmp/sysroots/qemuarm/usr/lib/pkgconfig

And then anyone requires ncurses.pc will fail.

The configure.in checks:
[snip]
if test -n "$PKG_CONFIG_LIBDIR" && test -d "$PKG_CONFIG_LIBDIR" ; then
[snip]

Create PKG_CONFIG_LIBDIR in do_configure will fix the problem.

We can reproduce the problem by:
Set SSTATE_DIR=/path/to/sstate-cache
1) In build1, make sure everything is ready in SSTATE_DIR
$ bitbake ncurses
2) In build2, rebuild ncurses only:
$ bitbake ncurses -ccleansstate && bitbake ncurses

Then we will see the warning in log.do_configure.

(From OE-Core rev: ea4010c8398745736b0c22ed037604db8fc43212)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>