x86: fix clang .macro retention check

x86: fix clang .macro retention check

There were two problems here: The first closing parentheses got parsed
by make to end the $(call invocation, and the escaping of the quotes
wasn't right either, as there's nowhere they would get un-escaped.

Furthermore there appears to be a puzzling problem with \n getting
expanded to an actual newline too early in some environments. Convert
these to semicolons at the same time.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Roger Pau Monné <roger.pau@citrix.com> [On FreeBSD and Debian 9.5]
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>