nativesdk: Set PKG_CONFIG_SYSTEM_ variables

When building nativesdk recipes, we noticed paths going into .pc files
which should have been suppressed since these were standard library
search paths. pkgconfig-native sets these variables to sane values
for native recipes, we need it set to values for our specific library
paths in the nativesdk case.

Setting these values cleans up the .pc files and suppresses the paths.

(From OE-Core rev: 837c8b749b06457ba4a5a76a34ffe45d36bf4ef3)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/nativesdk.bbclass

@@ -60,6 +60,8 @@ sbindir = "${bindir}"
 
 export PKG_CONFIG_DIR = "${STAGING_DIR_HOST}${libdir}/pkgconfig"
 export PKG_CONFIG_SYSROOT_DIR = "${STAGING_DIR_HOST}"
+export PKG_CONFIG_SYSTEM_LIBRARY_PATH = "${base_libdir}:${libdir}"
+export PKG_CONFIG_SYSTEM_INCLUDE_PATH = "${includedir}"
 
 python nativesdk_virtclass_handler () {
     pn = e.data.getVar("PN", True)