syscall: remove "use" function and calls from generated code.
Update syscall code generators to set build tags.
Regenerate zsyscall files, which makes the following changes:
- remove calls to "use"
- update build tags, adding missing ones in some cases
- "stat" renamed to "st" in some cases
- "libc_Utimes" renamed "libc_utimes" in one case
I'll mirror this change to x/sys/unix once committed.
Change-Id: Ic07e0ae1433dd133eb57e8dd2a3b86a62aab4eda
Reviewed-on: https://go-review.googlesource.com/36616
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>