bdwgc-native: Add missing pkgconfig DEPENDS

This fixes configure errors like:

| configure.ac:70: error: possibly undefined macro: AC_MSG_ERROR
|       If this token and others are legitimate, please use m4_pattern_allow.
|       See the Autoconf documentation.
| configure.ac:358: error: possibly undefined macro: AS_IF

Reproduced with bitbake bdwgc-native pkgconfig-native -c clean; bitbake bdwgc-native

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