[klibc] Kbuild: Fix the compiler execstack option

The compiler driver does not add any dashes to the options
given to -Wa, so we need to use either -Wa,--execstack or
-Wa,--noexecstack.

(I had this working some time ago, so I don't know how I ended up
committing the broken version.)

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
1 file changed