get rid of generic instances of asm/exec.h

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/sh/include/asm/Kbuild

@@ -7,6 +7,7 @@ generic-y += delay.h
 generic-y += div64.h
 generic-y += emergency-restart.h
 generic-y += errno.h
+generic-y += exec.h
 generic-y += fcntl.h
 generic-y += ioctl.h
 generic-y += ipcbuf.h