build: Fix including WHOLE_STATIC_LIBRARIES in static libraries

Static libraries that include other static libraries were being incorrectly
built with .a files inside the top level .a file, as well as the .o files
that were extracted from the component .a files.  This patch fixes the
final ar call to only add .o files to the archive.

Change-Id: Ic1ff025129e3c379fa56b4da2f09e9f16ea3c4fb