fix linux CGO flags for go 1.10

[jasonhancock]

Building on linux with go 1.10 leads to:

github.com/crewjam/go-xmlsec: invalid flag in #cgo CFLAGS: -w

[jasonhancock]

As a workaround:

CGO_CFLAGS_ALLOW='-w|-UXMLSEC_CRYPTO_DYNAMIC_LOADING' go build -o /tmp/foo

[avvari-da]

github.com/<username>/<repo_name>/vendor/github.com/crewjam/go-xmlsec: invalid flag in #cgo CFLAGS: -UXMLSEC_CRYPTO_DYNAMIC_LOADING

Am getting this error. Can anyone please help?

[savp-RP]

@dheeraj2dj Other issue provides a temporary workaround for this. #19