test: fix memcombine tests
test: fix memcombine tests

Two tests (load_le_byte8_uint64_inv and load_be_byte8_uint64)
pass but the generated code isn't actually correct.

The test regexp provides a false negative, as it matches the
MOVQ (SP), BP instruction in the epilogue.

Combined loads never worked for these cases - the test was added in error
as part of a batch and not noticed because of the above false match.

Normalize the amd64/386 tests to always negative match on narrower
loads and OR.

Change-Id: I256861924774d39db0e65723866c81df5ab5076f
Reviewed-on: https://go-review.googlesource.com/c/go/+/166837
Run-TryBot: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

nawawi/go,cloudflare/go,josharian/go,josharian/go,akutz/go,akutz/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go,josharian/go,cloudflare/go,nawawi/go,golang/go,josharian/go,CAFxX/go,akutz/go,josharian/go,josharian/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,golang/go,CAFxX/go,golang/go,josharian/go,akutz/go,CAFxX/go,josharian/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,akutz/go,cloudflare/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go