openjdk-7: inherit pkgconfig

Building OpenJDK-7 in Yocto 1.7 (Dizzy) quits with errors as follows. Inheriting pkgconfig fixes this problem.
.../configure: line 8645: syntax error near unexpected token `NSS,'
.../configure: line 8645: `PKG_CHECK_MODULES(NSS, nss, NSS_FOUND=yes, NSS_FOUND=no)'