unix: restore gccgo support

Initially added in https://golang.org/cl/9842 and
subsequently broken in https://golang.org/cl/85756.

Fixes golang/go#23361

Change-Id: Id458efdb4a9ffc5f038b4070fd514de9f78c17d7
Reviewed-on: https://go-review.googlesource.com/86755
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/gccgo.go

@@ -11,9 +11,19 @@ import "syscall"
 // We can't use the gc-syntax .s files for gccgo. On the plus side
 // much of the functionality can be written directly in Go.
 
+//extern gccgoRealSyscallNoError
+func realSyscallNoError(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r uintptr)
+
 //extern gccgoRealSyscall
 func realSyscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r, errno uintptr)
 
+func SyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	syscall.Entersyscall()
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	syscall.Exitsyscall()
+	return r, 0
+}
+
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
 	syscall.Entersyscall()
 	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
@@ -35,6 +45,11 @@ func Syscall9(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr,
 	return r, 0, syscall.Errno(errno)
 }
 
+func RawSyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	return r, 0
+}
+
 func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
 	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
 	return r, 0, syscall.Errno(errno)

unix/gccgo_c.c

@@ -31,6 +31,12 @@ gccgoRealSyscall(uintptr_t trap, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintp
 	return r;
 }
 
+uintptr_t
+gccgoRealSyscallNoError(uintptr_t trap, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4, uintptr_t a5, uintptr_t a6, uintptr_t a7, uintptr_t a8, uintptr_t a9)
+{
+	return syscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9);
+}
+
 // Define the use function in C so that it is not inlined.
 
 extern void use(void *) __asm__ (GOSYM_PREFIX GOPKGPATH ".use") __attribute__((noinline));