syscall: provide and use fcntlPtr for all BSD platforms

Provide fcntlPtr for all BSD platforms, then use this for FcntlFlock.
This reduces darwin and openbsd specific code, as well as avoiding
the use of an indirect system call on OpenBSD.

Updates #63900

Change-Id: I5c701f0d8413fab5477b9e21381395621d1fb6d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/540018
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Josh Rickmar <jrick@zettaport.com>

src/syscall/flock_darwin.go → src/syscall/flock_bsd.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build darwin || dragonfly || freebsd || netbsd || openbsd
+
 package syscall
 
 import "unsafe"

src/syscall/flock.go → src/syscall/flock_linux.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build linux || freebsd || openbsd || netbsd || dragonfly
-
 package syscall
 
 import "unsafe"

src/syscall/mksyscall.pl

@@ -284,6 +284,7 @@ ($)
 	if($libc) {
 		if($funcname eq "") {
 			$sysname = substr $sysname, 4;
+			$sysname =~ y/A-Z/a-z/;
 			$funcname = "libc_$sysname";
 		}
 		$sysname = "abi.FuncPCABI0(${funcname}_trampoline)";

src/syscall/syscall_bsd.go

@@ -515,6 +515,7 @@ func Futimes(fd int, tv []Timeval) (err error) {
 }
 
 //sys	fcntl(fd int, cmd int, arg int) (val int, err error)
+//sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_FCNTL
 
 var mapper = &mmapper{
 	active: make(map[*byte][]byte),

src/syscall/syscall_darwin.go

@@ -216,7 +216,6 @@ func Kill(pid int, signum Signal) (err error) { return kill(pid, int(signum), 1)
 //sysnb execve(path *byte, argv **byte, envp **byte) (err error)
 //sysnb exit(res int) (err error)
 //sys	sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error)
-//sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_fcntl
 //sys   unlinkat(fd int, path string, flags int) (err error)
 //sys   openat(fd int, path string, flags int, perm uint32) (fdret int, err error)
 //sys	getcwd(buf []byte) (n int, err error)

src/syscall/syscall_openbsd_libc.go

@@ -68,6 +68,5 @@ func syscall9X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr,
 //sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
 //sysnb getentropy(p []byte) (err error)
 //sys   fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
-//sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_fcntl
 //sys   unlinkat(fd int, path string, flags int) (err error)
 //sys   openat(fd int, path string, flags int, perm uint32) (fdret int, err error)