linux: use correct libgcrypt-config paths when cross-compiling

build/linux/libgcrypt-config-wrapper

Index: build/linux/libgcrypt-config-wrapper
diff --git a/build/linux/libgcrypt-config-wrapper b/build/linux/libgcrypt-config-wrapper
new file mode 100755
index 0000000000000000000000000000000000000000..48a2a8e59fb2fb3c5c84c24b6265d2c12793776b
--- /dev/null
+++ b/build/linux/libgcrypt-config-wrapper
@@ -0,0 +1,17 @@
+#!/bin/bash
+
+# This program wraps around libgcrypt-config to generate the correct include and
+# library paths when cross-compiling using a sysroot.
+
+sysroot="$1"
+shift
+
+if [ -z "$sysroot" ]
+then
+  echo "usage: $0 /path/to/sysroot [libgcrypt-config-arguments]" >&2
+  exit 1
+fi
+
+config_path=$sysroot/usr/bin/libgcrypt-config
+set -e
+echo `$config_path "$@" | sed -e 's|/|'$sysroot'/|'`