internal/core: fix build on Solaris

Solaris has unix.Mmap but not syscall.Mmap.

Change-Id: Ia48b1db21d48caa835e43ea4f6616c8c3d06e089
Reviewed-on: https://go-review.googlesource.com/c/debug/+/170786
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
diff --git a/go.mod b/go.mod
index aa1a658..addabf8 100644
--- a/go.mod
+++ b/go.mod
@@ -9,5 +9,5 @@
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect
 	github.com/spf13/cobra v0.0.3
 	github.com/spf13/pflag v1.0.3 // indirect
-	golang.org/x/sys v0.0.0-20190312061237-fead79001313 // indirect
+	golang.org/x/sys v0.0.0-20190312061237-fead79001313
 )
diff --git a/internal/core/process_unix.go b/internal/core/process_unix.go
index 3817678..9ca644b 100644
--- a/internal/core/process_unix.go
+++ b/internal/core/process_unix.go
@@ -6,10 +6,14 @@
 
 package core
 
-import "syscall"
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
 
 func init() {
 	mapFile = func(fd int, offset int64, length int) (data []byte, err error) {
-		return syscall.Mmap(fd, offset, length, syscall.PROT_READ, syscall.MAP_SHARED)
+		return unix.Mmap(fd, offset, length, syscall.PROT_READ, syscall.MAP_SHARED)
 	}
 }