build-sys: don't use -Wcast-align anymore

We do a lot of these casts, and they are all OK, so let's get rid of the
warning, to make things quieter.

http://lists.freedesktop.org/archives/systemd-devel/2014-February/017174.html

autogen.sh

@@ -63,7 +63,7 @@ elif [ "x$1" = "xa" ]; then
         ./configure CFLAGS='-g -O0 -Wsuggest-attribute=pure -Wsuggest-attribute=const -ftrapv' --enable-compat-libs --enable-kdbus $args
         make clean
 elif [ "x$1" = "xl" ]; then
-        ./configure CC=clang CFLAGS='-g -O0 -ftrapv -Wno-cast-align -Wno-gnu' --enable-compat-libs --enable-kdbus $args
+        ./configure CC=clang CFLAGS='-g -O0 -ftrapv -Wno-gnu' --enable-compat-libs --enable-kdbus $args
         make clean
 elif [ "x$1" = "xs" ]; then
         scan-build ./configure CFLAGS='-g -O0 -ftrapv' --enable-compat-libs --enable-kdbus $args

configure.ac

@@ -137,7 +137,6 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
         -Wmissing-noreturn \
         -Wshadow \
         -Wendif-labels \
-        -Wcast-align \
         -Wstrict-aliasing=2 \
         -Wwrite-strings \
         -Wno-long-long \