syscall: fix stack frame sizes in assembly

for GOOS in darwin freebsd linux nacl netbsd openbsd plan9 solaris windows
do
        for GOARCH in 386 amd64 amd64p32 arm
        do
                go vet
        done
done

These are all real mistakes being corrected, but none
of them should be able to cause problems today
due to the NOSPLIT on the functions.

However, vet has also identified a few important problems.
I'm sending this CL to get rid of the trivial 'go vet' results
before attacking the real ones.

LGTM=r
R=golang-codereviews, r, bradfitz
CC=golang-codereviews
https://golang.org/cl/95460046

src/pkg/syscall/syscall_linux_386.go

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// TODO(rsc): Rewrite all nn(SP) references into name+(nn-8)(FP)
+// so that go vet can check that they are correct.
+
 package syscall
 
 import "unsafe"