cmake: add --divide to GNU assembler options for x86

GNU Assembler, by default on non-Linux targets, treats slashes as
start of comments on i386.
(https://sourceware.org/binutils/docs-2.33.1/as/i386_002dChars.html#i386_002dChars

)
In order to use division, `--divide` needs to be passed to
the assembler.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>