alsa-lib: fix build on powerpc64 and powerpc64le

Fixes linker error
http://autobuild.buildroot.net/results/c6272ac900d1a53b976839ac4f50a210b3e6b354



On powerpc64 (and powerpc64le) the build fails due to linker problems
because of an old (2003) workaround for powerpc64, presumably working
around an old toolchain problem that is no longer present. Removing
the workaround allows the build to succeed. A new patch is added for
this.

Additionally, there was a mistake in patch 3: the patch added a test
for HAVE_LIBDL to include/alsa-symbols.h but it was positioned in the
file before config.h was included, so HAVE_LIBDL is never seen as
defined.  The test was also using HAVE_LIBDL (which indicates the
library) rather than HAVE_DLFCN (which indicates the header).

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>