configure.ac: set CFLAGS and friends to -O0 if gcov is being used add GCOV LIBS

configure.ac: set CFLAGS and friends to -O0 if gcov is being used add GCOV LIBS

Original commit message from CVS:
* configure.ac:
set CFLAGS and friends to -O0 if gcov is being used
add GCOV LIBS
* gst/Makefile.am:
* libs/gst/base/Makefile.am:
* libs/gst/check/Makefile.am:
* libs/gst/controller/Makefile.am:
* libs/gst/dataprotocol/Makefile.am:
* libs/gst/net/Makefile.am:
* plugins/elements/Makefile.am:
* plugins/indexers/Makefile.am:
add makefile rules to generate gcov data and clean up
* tests/check/Makefile.am:
add a coverage target that generates an html overview
of coverage data