gst-arch.m4: fix unaligned detection for x86-64 when cross compiling

gst-arch.m4: fix unaligned detection for x86-64 when cross compiling

Commit 4221e9dc (amd64/x86_64 allows unaligned memory access too) added
x86-64 to the unaligned access whitelist, but missed the trailing
wildcards, so the test never succeeds (host is something like
x86_64-unknown-linux-gnu).

When building natively, this isn't a big deal as the AC_TRY_RUN test
correctly detects it, but that doesn't work when cross compiling so
the build dies with:

configure: error: cannot run test program while cross compiling
See `config.log' for more details.

Fix it by adding the trailing wildcards.

Fixes bug #607317.