doc: - some more plan 9 disas examples - x86 callconv doc updated: * mainly info about aggregate passing and returning * removing section about pascal calling convention, as dyncall doesn't support 16bit abis - some cleanups

#!/bin/sh
`which gcc || which clang` -E -P -DGEN_MASM ${1:?Usage: $0 <name> [<outsuffix>]}.S \
	| sed "/^$/d;1i\\
; auto-generated by `basename $0`
;s/$/
/" \
	> $1$2.asm