set intel SSE features in gf_internal_t::sse at runtime

When running on a processor different from the one used at compile time,
the sse field will contain the process capabilities evaluated at
runtime.

The sse bitfield is set at compile time as a first step and will be set
at runtime in another commit implementing something similar to what Ceph
does https://github.com/ceph/ceph/blob/firefly/src/arch/intel.c#L10

Signed-off-by: Loic Dachary <loic@dachary.org>
w128: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
w64: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
w32: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
w16: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
w8: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
w4: select SSE features at runtime

Signed-off-by: Loic Dachary <loic@dachary.org>
AX_SSE detects the compiler SSE capabilities

For each SSE feature supported by the compiler

* add the corresponding -msse* flag
* define HAVE_SSE*

Remove AX_EXT because it decides based on the CPU capabilities of the
machine compiling the binary which may or may not be the one running
them.

Signed-off-by: Loic Dachary <loic@dachary.org>
create a .gitignore

Signed-off-by: Loic Dachary <loic@dachary.org>