contrib: add /usr/lib/TRIPLET/pkgconfig to PKG_CONFIG_LIBDIR

Not sure if it's distro dependant but the Raspbian packages are found in
/usr/lib/arm-linux-gnueabihf/pkgconfig

contrib/src/main.mak

@@ -229,7 +229,7 @@ ifdef HAVE_CROSS_COMPILE
 # This inhibits .pc file from within the cross-compilation toolchain sysroot.
 # Hopefully, nobody ever needs that.
 PKG_CONFIG_PATH := /usr/share/pkgconfig
-PKG_CONFIG_LIBDIR := /usr/$(HOST)/lib/pkgconfig
+PKG_CONFIG_LIBDIR := /usr/$(HOST)/lib/pkgconfig:/usr/lib/$(HOST)/pkgconfig
 export PKG_CONFIG_LIBDIR
 endif
 PKG_CONFIG_PATH := $(PREFIX)/lib/pkgconfig:$(PKG_CONFIG_PATH)