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

---

index 46e5257..2ba7aa5 100644
@@ -34,5 +34,5 @@ S = "${WORKDIR}/gc-${REAL_PV}"
 
 ARM_INSTRUCTION_SET = "arm"
 
-inherit autotools
+inherit autotools pkgconfig
 BBCLASSEXTEND = "native nativesdk"