linux-user, x86_64: add syscall table generation support

Copy syscall_64.tbl and syscallhdr.sh from linux/arch/x86/kernel/syscalls v5.5
Update syscallhdr.sh to generate QEMU syscall_nr.h

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20200310103403.3284090-16-laurent@vivier.eu>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/x86_64/syscallhdr.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+in="$1"
+out="$2"
+my_abis=`echo "($3)" | tr ',' '|'`
+prefix="$4"
+offset="$5"
+
+fileguard=LINUX_USER_X86_64_`basename "$out" | sed \
+    -e 'y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/' \
+    -e 's/[^A-Z0-9_]/_/g' -e 's/__/_/g'`
+grep -E "^[0-9A-Fa-fXx]+[[:space:]]+${my_abis}" "$in" | sort -n | (
+    echo "#ifndef ${fileguard}"
+    echo "#define ${fileguard} 1"
+    echo ""
+
+    while read nr abi name entry ; do
+    if [ -z "$offset" ]; then
+        echo "#define TARGET_NR_${prefix}${name} $nr"
+    else
+        echo "#define TARGET_NR_${prefix}${name} ($offset + $nr)"
+        fi
+    done
+
+    echo ""
+    echo "#endif /* ${fileguard} */"
+) > "$out"